spring-framework/spring-framework-reference/src/jdbc.xml

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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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<chapter id="jdbc">
  <title>Data access with JDBC</title>

  <section id="jdbc-introduction">
    <title>Introduction to Spring Framework JDBC</title>

    <para>The value-add provided by the Spring Framework JDBC abstraction is
    perhaps best shown by the sequence of actions outlined in the table
    below. The table shows what actions Spring will take care of and which
    actions are the responsibility of you, the application developer.<!--Is this sequence correct, as far as what developer does and doesn't do? Does it adhere to info in the rest of the chapter?
--><!--How does JDBC know what connection parameters are if a human does not at some point define them?--><!--TR: OK. I have rewritten this as a table indicating who has what responsibility. --></para>

    <table align="left" width="">
      <title>Spring JDBC - who does what?</title>

      <tgroup cols="3">
        <colspec colnum="1" colwidth="350" />

        <colspec colnum="2" colwidth="40" />

        <colspec colnum="3" colwidth="40" />

        <thead>
          <row>
            <entry align="center">Action</entry>

            <entry align="center">Spring</entry>

            <entry align="center">You</entry>
          </row>
        </thead>

        <tbody>
          <row>
            <entry>Define connection parameters.</entry>

            <entry align="center"><emphasis role="bold"></emphasis></entry>

            <entry align="center">X</entry>
          </row>

          <row>
            <entry>Open the connection.</entry>

            <entry align="center">X</entry>

            <entry align="center"></entry>
          </row>

          <row>
            <entry>Specify the SQL statement.</entry>

            <entry align="center"></entry>

            <entry align="center">X</entry>
          </row>

          <row>
            <entry>Declare parameters and provide parameter values</entry>

            <entry align="center"></entry>

            <entry align="center">X</entry>
          </row>

          <row>
            <entry>Prepare and execute the statement.</entry>

            <entry align="center">X</entry>

            <entry align="center"></entry>
          </row>

          <row>
            <entry>Set up the loop to iterate through the results (if
            any).</entry>

            <entry align="center">X</entry>

            <entry align="center"></entry>
          </row>

          <row>
            <entry>Do the work for each iteration.</entry>

            <entry align="center"></entry>

            <entry align="center">X</entry>
          </row>

          <row>
            <entry>Process any exception.</entry>

            <entry align="center">X</entry>

            <entry align="center"></entry>
          </row>

          <row>
            <entry>Handle transactions.</entry>

            <entry align="center">X</entry>

            <entry align="center"></entry>
          </row>

          <row>
            <entry>Close the connection, statement and resultset.</entry>

            <entry align="center">X</entry>

            <entry align="center"></entry>
          </row>
        </tbody>
      </tgroup>
    </table>

    <para>The Spring Framework takes care of all the low-level details that
    can make JDBC such a tedious API to develop with.</para>

    <section id="jdbc-choose-style">
      <title>Choosing an approach for JDBC database access</title>

      <para>You can choose among several approaches to form the basis for your
      JDBC database access. In addition to three flavors of the JdbcTemplate,
      a new SimpleJdbcInsert and SimplejdbcCall approach optimizes database
      metadata, and the RDBMS Object style takes a more object-oriented
      approach similar to that of JDO Query design. Once you start using one
      of these approaches, you can still mix and match to include a feature
      from a different approach. All approaches require a JDBC 2.0-compliant
      driver, and some advanced features require a JDBC 3.0 driver.</para>

      <note>
        <para>Spring 3.0 updates all of the following approaches with Java 5
        support such as generics and varargs.<!--Is there a formal name for varargs? Is this written correctly?I've inserted this note to avoid redundancy below.--></para>
      </note>

      <itemizedlist>
        <listitem>
          <para><emphasis role="bold">JdbcTemplate</emphasis> is the classic
          Spring JDBC approach and the most popular. This "lowest level"
          approach and all others use a JdbcTemplate under the covers, and all
          are updated with Java 5 support such as generics and varargs.</para>
        </listitem>

        <listitem>
          <para><emphasis role="bold">NamedParameterJdbcTemplate</emphasis>
          wraps a <code>JdbcTemplate</code> to provide named parameters
          instead of the traditional JDBC "?" placeholders. This approach
          provides better documentation and ease of use when you have multiple
          parameters for an SQL statement.</para>
        </listitem>

        <listitem>
          <para><emphasis role="bold">SimpleJdbcTemplate</emphasis> combines
          the most frequently used operations of JdbcTemplate and
          NamedParameterJdbcTemplate.</para>
        </listitem>

        <listitem>
          <para><emphasis role="bold">SimpleJdbcInsert and
          SimpleJdbcCall</emphasis> optimize database metadata to limit the
          amount of necessary configuration. This approach simplifies coding
          so that you only need to provide the name of the table or procedure
          and provide a map of parameters matching the column names. <!--Revise preceding to clarify: You *must* use this approach w/ SimpleJdbcTemplate, it is *recommended*, or you *can*? 
TR: OK. I removed the sentence since it isn;t entirely accurate. The implementation uses a plain JdbcTemplate internally.-->
          This only works if the database provides adequate metadata. If the
          database doesn't provide this metadata, you will have to provide
          explicit configuration of the parameters.</para>
        </listitem>

        <listitem>
          <para><emphasis role="bold">RDBMS Objects including MappingSqlQuery,
          SqlUpdate and StoredProcedure</emphasis> requires you to create
          reusable and thread-safe objects during initialization of your data
          access layer. This approach is modeled after JDO Query wherein you
          define your query string, declare parameters, and compile the query.
          Once you do that, execute methods can be called multiple times with
          various parameter values passed in.</para>
        </listitem>
      </itemizedlist>
    </section>

    <section id="jdbc-packages">
      <title>Package hierarchy<!--I have provided links to main sections that deal with most packages. TR: OK--></title>

      <para>The Spring Framework's JDBC abstraction framework consists of four
      different packages, namely <literal>core</literal>,
      <literal>datasource</literal>, <literal>object</literal>, and
      <literal>support</literal>.</para>

      <para>The <literal>org.springframework.jdbc.core</literal> package
      contains the <classname>JdbcTemplate</classname> class and its various
      callback interfaces, plus a variety of related classes. A subpackage
      named <literal>org.springframework.jdbc.core.simple</literal> contains
      the <classname>SimpleJdbcTemplate</classname> class and the related
      <classname>SimpleJdbcInsert</classname> and
      <classname>SimpleJdbcCall</classname> classes. Another subpackage named
      <literal>org.springframework.jdbc.core.namedparam</literal> contains the
      <classname>NamedParameterJdbcTemplate</classname> class and the related
      support classes. See <xref linkend="jdbc-core" />, <xref
      linkend="jdbc-advanced-jdbc" />, and <xref
      linkend="jdbc-simple-jdbc" /></para>

      <para>The <literal>org.springframework.jdbc.datasource</literal> package
      contains a utility class for easy
      <interfacename>DataSource</interfacename> access, and various simple
      <interfacename>DataSource</interfacename> implementations that can be
      used for testing and running unmodified JDBC code outside of a Java EE
      container. A subpackage named
      <literal>org.springfamework.jdbc.datasource.embedded</literal> provides
      support for creating in-memory database instances using Java database
      engines such as HSQL and H2. See <xref linkend="jdbc-connections" /> and
      <xref linkend="jdbc-embedded-database-support" /></para>

      <para>The <literal>org.springframework.jdbc.object</literal> package
      contains classes that represent RDBMS queries, updates, and stored
      procedures as thread safe, reusable objects. See <xref
      linkend="jdbc-object" />.This approach is modeled by JDO, although of
      course objects returned by queries are <quote>disconnected</quote> from
      the database. This higher level of JDBC abstraction depends on the
      lower-level abstraction in the
      <literal>org.springframework.jdbc.core</literal> package.</para>

      <para><!--Need x-ref for preceding and next sentences. TR: Revised, please review. Combined to single paragraph about exception translation.-->The
      <literal>org.springframework.jdbc.support</literal> package provides
      <classname>SQLException</classname> translation functionality and some
      utility classes. Exceptions thrown during JDBC processing are translated
      to exceptions defined in the <literal>org.springframework.dao</literal>
      package. This means that code using the Spring JDBC abstraction layer
      does not need to implement JDBC or RDBMS-specific error handling. All
      translated exceptions are unchecked, which gives you the option of
      catching the exceptions from which you can recover while allowing other
      exceptions to be propagated to the caller. See <xref
      linkend="jdbc-SQLExceptionTranslator" />.</para>
    </section>
  </section>

  <section id="jdbc-core">
    <title>Using the JDBC core classes to control basic JDBC processing and
    error handling<!--Note: I moved the *DataSource* subsection out of this section because it seems to belong more under *Controlling database connections.*--><!--This section here is about core classes, but datasource is a separate package from core. See *Package hierarchy* section above. TR: OK--></title>

    <section id="jdbc-JdbcTemplate">
      <title><classname>JdbcTemplate</classname></title>

      <para>The <classname>JdbcTemplate</classname> class is the central class
      in the JDBC core package. It handles the creation and release of
      resources, which helps you avoid common errors such as forgetting to
      close the connection. It performs the basic tasks of the core JDBC
      workflow such as statement creation and execution, leaving application
      code to provide SQL and extract results. The
      <classname>JdbcTemplate</classname> class executes SQL queries, update
      statements and stored procedure calls, performs iteration over
      <interfacename>ResultSet</interfacename>s and extraction of returned
      parameter values.<!--The wording of the preceding sentence does not track. Which is correct: the class *executes* queries, *updated* statements, --><!--and stored procedure calls...OR the class *executes* queries and *updates* statements and stored procedure calls. Second part of--><!--sentence; is this clear? It *imitates* iteration and extraction? TR: Revised, please review. The class executes *SQL queries*,  *update statements* or *stored procedure calls* ...-->
      It also catches JDBC exceptions and translates them to the generic, more
      informative, exception hierarchy defined in the
      <literal>org.springframework.dao</literal> package.</para>

      <para>When you use the <classname>JdbcTemplate</classname> for your
      code, you only need to implement callback interfaces, giving them a
      clearly defined contract. The
      <interfacename>PreparedStatementCreator</interfacename> callback
      interface creates a prepared statement given a
      <interfacename>Connection</interfacename> provided by this class,
      providing SQL and any necessary parameters. The same is true for the
      <interfacename>CallableStatementCreator</interfacename> interface, which
      creates callable statements. The
      <interfacename>RowCallbackHandler</interfacename> interface extracts
      values from each row of a
      <interfacename>ResultSet</interfacename>.</para>

      <!--and stored procedure calls? TR: they are handled by the CallableStatement; Queries and update statements are handled by PreparedStatement.-->

      <para>The <classname>JdbcTemplate</classname> can be used within a DAO
      implementation through direct instantiation with a
      <interfacename>DataSource</interfacename> reference, or be configured in
      a Spring IoC container and given to DAOs as a bean reference. <note>
          <para>The <interfacename>DataSource</interfacename> should always be
          configured as a bean in the Spring IoC container. In the first case
          the bean is given to the service directly; in the second case it is
          given to the prepared template.<!--I've revised so that it reads better, but please clarify second sentence: Specify what *the first case* is, what--><!--do you mean by *is given* and it's given to *which* service? First mention of a service. Specify what *second--><!-- case* is and what you mean by *is given*. TR: OK.--></para>
        </note></para>

      <para>All SQL issued by this class is logged at the
      <literal>DEBUG</literal> level under the category corresponding to the
      fully qualified class name of the template instance (typically
      <classname>JdbcTemplate</classname>, but it may be different if you are
      using a custom subclass of the <classname>JdbcTemplate</classname>
      class).</para>

      <section id="jdbc-JdbcTemplate-examples">
        <title>Examples of JdbcTemplate class usage</title>

        <para>This section provides some examples of
        <classname>JdbcTemplate</classname> class usage. These examples are
        not an exhaustive list of all of the functionality exposed by the
        <classname>JdbcTemplate</classname>; see the attendant Javadocs for
        that.</para>

        <section id="jdbc-JdbcTemplate-examples-query">
          <title>Querying (SELECT)</title>

          <para>Here is a simple query for getting the number of rows in a
          relation:</para>

          <programlisting language="java">int rowCount = this.jdbcTemplate.queryForInt("select count(*) from t_actor");</programlisting>

          <para>A simple query using a bind variable:</para>

          <programlisting language="java">int countOfActorsNamedJoe = this.jdbcTemplate.queryForInt(
        "select count(*) from t_actor where first_name = ?", "Joe");</programlisting>

          <para>Querying for a <classname>String</classname>:</para>

          <programlisting language="java">String lastName = this.jdbcTemplate.queryForObject(
        "select last_name from t_actor where id = ?", 
        new Object[]{1212L}, String.class);</programlisting>

          <para>Querying and populating a <emphasis>single</emphasis> domain
          object:</para>

          <programlisting language="java">Actor actor = this.jdbcTemplate.queryForObject(
        "select first_name, last_name from t_actor where id = ?",
        new Object[]{1212L},
        new RowMapper&lt;Actor&gt;() {
            public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {
                Actor actor = new Actor();
                actor.setFirstName(rs.getString("first_name"));
                actor.setLastName(rs.getString("last_name"));
                return actor;
            }
        });
</programlisting>

          <para>Querying and populating a number of domain objects:</para>

          <programlisting language="java">List&lt;Actor&gt; actors = this.jdbcTemplate.query(
        "select first_name, last_name from t_actor",
        new RowMapper&lt;Actor&gt;() {
            public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {
                Actor actor = new Actor();
                actor.setFirstName(rs.getString("first_name"));
                actor.setLastName(rs.getString("last_name"));
                return actor;
            }
        });
</programlisting>

          <para>If the last two snippets of code actually existed in the same
          application, it would make sense to remove the duplication present
          in the two <interfacename>RowMapper</interfacename> anonymous inner
          classes, and extract them out into a single class (typically a
          <literal>static</literal> inner class) that can then be referenced
          by DAO methods as needed. For example, it may be better to write the
          last code snippet as follows:</para>

          <programlisting language="java">public List&lt;Actor&gt; findAllActors() {
    return this.jdbcTemplate.query( "select first_name, last_name from t_actor", new ActorMapper());
}

private static final class ActorMapper implements RowMapper&lt;Actor&gt; {

    public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {
        Actor actor = new Actor();
        actor.setFirstName(rs.getString("first_name"));
        actor.setLastName(rs.getString("last_name"));
        return actor;
    }        
}</programlisting>
        </section>

        <section id="jdbc-JdbcTemplate-examples-update">
          <title>Updating (INSERT/UPDATE/DELETE) with jdbcTemplate<!--Provide introductory text as with other examples. TR: OK.--></title>

          <para>You use the <methodname>update(..)</methodname> method to
          perform insert, update and delete operations. Parameter values are
          usually provided as var args or alternatively as an object
          array.</para>

          <programlisting language="java">this.jdbcTemplate.update(
        "insert into t_actor (first_name, last_name) values (?, ?)", 
        "Leonor", "Watling");</programlisting>

          <programlisting language="java">this.jdbcTemplate.update(
        "update t_actor set = ? where id = ?", 
        "Banjo", 5276L);</programlisting>

          <programlisting language="java">this.jdbcTemplate.update(
        "delete from actor where id = ?",
        Long.valueOf(actorId));</programlisting>
        </section>

        <section id="jdbc-JdbcTemplate-examples-other">
          <title>Other jdbcTemplate operations</title>

          <para>You can use the <methodname>execute(..)</methodname> method to
          execute any arbitrary SQL, and as such the method is often used for
          DDL statements. It is heavily overloaded with variants taking
          callback interfaces, binding variable arrays, and so on.</para>

          <programlisting language="java">this.jdbcTemplate.execute("create table mytable (id integer, name varchar(100))");</programlisting>

          <para>The following example invokes a simple stored procedure. More
          sophisticated stored procedure support is <link
          linkend="jdbc-StoredProcedure">covered later</link>.</para>

          <programlisting language="java">this.jdbcTemplate.update(
        "call SUPPORT.REFRESH_ACTORS_SUMMARY(?)", 
        Long.valueOf(unionId));</programlisting>
        </section>
      </section>

      <section id="jdbc-JdbcTemplate-idioms">
        <title><classname>JdbcTemplate</classname> best practices</title>

        <para>Instances of the <classname>JdbcTemplate</classname> class are
        <emphasis>threadsafe once configured</emphasis>. This is important
        because it means that you can configure a single instance of a
        <classname>JdbcTemplate</classname> and then safely inject this
        <emphasis>shared</emphasis> reference into multiple DAOs (or
        repositories). The <classname>JdbcTemplate</classname> is stateful, in
        that it maintains a reference to a
        <interfacename>DataSource</interfacename>, but this state is
        <emphasis>not</emphasis> conversational state.</para>

        <para>A common practice when using the
        <classname>JdbcTemplate</classname> class (and the associated <link
        linkend="jdbc-SimpleJdbcTemplate"><classname>SimpleJdbcTemplate</classname></link>
        and <link
        linkend="jdbc-NamedParameterJdbcTemplate"><classname>NamedParameterJdbcTemplate</classname></link>
        classes) is to configure a <interfacename>DataSource</interfacename>
        in your Spring configuration file, and then dependency-inject that
        shared <interfacename>DataSource</interfacename> bean into your DAO
        classes; the <classname>JdbcTemplate</classname> is created in the
        setter for the <interfacename>DataSource</interfacename>. This leads
        to DAOs that look in part like the following:</para>

        <programlisting language="java">public class JdbcCorporateEventDao implements CorporateEventDao {

    private JdbcTemplate jdbcTemplate;

    public void setDataSource(DataSource dataSource) {
        <emphasis role="bold">this.jdbcTemplate = new JdbcTemplate(dataSource);</emphasis>
    }

    <lineannotation>// JDBC-backed implementations of the methods on the <interfacename>CorporateEventDao</interfacename> follow...</lineannotation>
}</programlisting>

        <para>The corresponding configuration might look like this.</para>

        <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd"&gt;
    
    &lt;bean id="corporateEventDao" class="com.example.JdbcCorporateEventDao"&gt;
        &lt;property name="dataSource" ref="dataSource"/&gt;
    &lt;/bean&gt;
    
    &lt;bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"&gt;
        &lt;property name="driverClassName" value="${jdbc.driverClassName}"/&gt;
        &lt;property name="url" value="${jdbc.url}"/&gt;
        &lt;property name="username" value="${jdbc.username}"/&gt;
        &lt;property name="password" value="${jdbc.password}"/&gt;
    &lt;/bean&gt;

    &lt;context:property-placeholder location="jdbc.properties"/&gt;

&lt;/beans&gt;</programlisting>

        <para>An alternative to explicit configuration is to use
        component-scanning and annotation support for dependency injection. In
        this case you annotate the class with
        <interfacename>@Repository</interfacename> (which makes it a candidate
        for component-scanning) and annotate the
        <classname>DataSource</classname> setter method with
        <interfacename>@Autowired</interfacename>.<!--Re preceding sentence, I don't see @Autowired in next two examples. TR: OK AS IS. Made it *bold*--></para>

        <para><programlisting language="java"><emphasis role="bold">@Repository</emphasis>
public class JdbcCorporateEventDao implements CorporateEventDao {

    private JdbcTemplate jdbcTemplate;

    <emphasis role="bold">@Autowired</emphasis>
    public void setDataSource(DataSource dataSource) {
        <emphasis role="bold">this.jdbcTemplate = new JdbcTemplate(dataSource);</emphasis>
    }

    <lineannotation>// JDBC-backed implementations of the methods on the <interfacename>CorporateEventDao</interfacename> follow...</lineannotation>
}</programlisting></para>

        <para>The corresponding XML configuration file <!--*corresponding* to what? TR: to the prvious code-snippet-->would
        look like the following:</para>

        <para><programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd"&gt;
    
    &lt;!-- Scans within the base package of the application for @Components to configure as beans --&gt;
    &lt;context:component-scan base-package="org.springframework.docs.test" /&gt;
    
    &lt;bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"&gt;
        &lt;property name="driverClassName" value="${jdbc.driverClassName}"/&gt;
        &lt;property name="url" value="${jdbc.url}"/&gt;
        &lt;property name="username" value="${jdbc.username}"/&gt;
        &lt;property name="password" value="${jdbc.password}"/&gt;
    &lt;/bean&gt;

    &lt;context:property-placeholder location="jdbc.properties"/&gt;

&lt;/beans&gt;</programlisting>If you are using Spring's
        <classname>JdbcDaoSupport</classname> class, and your various
        JDBC-backed DAO classes extend from it, then your sub-class inherits a
        <methodname>setDataSource(..)</methodname> method from the
        <classname>JdbcDaoSupport</classname> class. <!--Revise to clarify what you mean by inheriting method *for free*. For free as opposed to what? Also you don't inherit, don't your--><!--subclasses inherit? TR: Revised, please review.-->You
        can choose whether to inherit from this class. The
        <classname>JdbcDaoSupport</classname> class is provided as a
        convenience only.</para>

        <para>Regardless of which of the above template initialization styles
        you choose to use (or not), it is seldom necessary to create a new
        instance of a <classname>JdbcTemplate</classname> class each time you
        want to execute SQL. Once configured, a
        <classname>JdbcTemplate</classname> instance is threadsafe. You may
        want multiple <classname>JdbcTemplate</classname> instances if your
        application accesses multiple databases, which requires multiple
        <interfacename>DataSources</interfacename>, and subsequently multiple
        differently configured <classname>JdbcTemplates</classname>.</para>
      </section>
    </section>

    <section id="jdbc-NamedParameterJdbcTemplate">
      <title><classname>NamedParameterJdbcTemplate</classname></title>

      <para>The <classname>NamedParameterJdbcTemplate</classname> class adds
      support for programming JDBC statements using named parameters, as
      opposed to programming JDBC statements using only classic placeholder
      (<literal>'?'</literal>) arguments. The
      <classname>NamedParameterJdbcTemplate</classname> class wraps a
      <classname>JdbcTemplate</classname>, and delegates to the wrapped
      <classname>JdbcTemplate</classname> to do much of its work. This section
      describes only those areas of the
      <classname>NamedParameterJdbcTemplate</classname> class that differ from
      the <classname>JdbcTemplate</classname> itself; namely, programming JDBC
      statements using named parameters.</para>

      <programlisting language="java"><lineannotation>// some JDBC-backed DAO class...</lineannotation>
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;

public void setDataSource(DataSource dataSource) {
    this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}

public int countOfActorsByFirstName(String firstName) {

    String sql = "select count(*) from T_ACTOR where first_name = :first_name";

    SqlParameterSource namedParameters = new MapSqlParameterSource("first_name", firstName);

    return namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}</programlisting>

      <para>Notice the use of the named parameter notation in the value
      assigned to the <literal>sql</literal> variable, and the corresponding
      value that is plugged into the <literal>namedParameters</literal>
      variable (of type <classname>MapSqlParameterSource</classname>).</para>

      <para>Alternatively, you can pass along named parameters and their
      corresponding values to a
      <classname>NamedParameterJdbcTemplate</classname> instance by using the
      <interfacename>Map</interfacename>-based style.<!--Revision ok? Clarify to say *Alternatively* you can pass along OR *In addition* you can pass along, to clarify whether you can do this--><!--instead of doing what sentence before it says to do, or in addition to doing it. This needs to be clear. TR: OK.-->The
      remaining methods exposed by the
      <interfacename>NamedParameterJdbcOperations</interfacename> and
      implemented by the <classname>NamedParameterJdbcTemplate</classname>
      class follow a similar pattern and are not covered here.</para>

      <para>The following example shows the use of the
      <interfacename>Map</interfacename>-based style.<!--Need an intro sentence to the following example. What does it show, what's its purpose? TR: OK.--></para>

      <programlisting language="java"><lineannotation>// some JDBC-backed DAO class...</lineannotation>
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;

public void setDataSource(DataSource dataSource) {
    this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}

public int countOfActorsByFirstName(String firstName) {

    String sql = "select count(*) from T_ACTOR where first_name = :first_name";

    Map namedParameters = Collections.singletonMap("first_name", firstName);

    return this.namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}</programlisting>

      <para>One nice feature related to the
      <classname>NamedParameterJdbcTemplate</classname> (and existing in the
      same Java package) is the <classname>SqlParameterSource</classname>
      interface. You have already seen an example of an implementation of this
      interface in one of the previous code snippet (the
      <classname>MapSqlParameterSource</classname> class). <!--Revision ok?Why say *another feature*? So far this is the only feature discussed for NamedParameterJDBC template. It's mentioned above.--><!--In next paragraph you do describe another implementation. --><!--TR: Revised, please review.--><interfacename>An
      <classname>SqlParameterSource</classname></interfacename> is a source of
      named parameter values to a
      <classname>NamedParameterJdbcTemplate</classname>. The
      <classname>MapSqlParameterSource</classname> class is a very simple
      implementation that is simply an adapter around a
      <interfacename>java.util.Map</interfacename>, where the keys are the
      parameter names and the values are the parameter values.</para>

      <para>Another <interfacename>SqlParameterSource</interfacename>
      implementation is the
      <classname>BeanPropertySqlParameterSource</classname> class. This class
      wraps an arbitrary JavaBean (that is, an instance of a class that
      adheres to <ulink
      url="http://java.sun.com/products/javabeans/docs/spec.html">the JavaBean
      conventions</ulink>), and uses the properties of the wrapped JavaBean as
      the source of named parameter values.</para>

      <programlisting language="java">public class Actor {

    private Long id;
    private String firstName;
    private String lastName;
    
    public String getFirstName() {
        return this.firstName;
    }
    
    public String getLastName() {
        return this.lastName;
    }
    
    public Long getId() {
        return this.id;
    }
    
    <lineannotation>// setters omitted...</lineannotation>

}</programlisting>

      <programlisting language="java"><lineannotation>// some JDBC-backed DAO class...</lineannotation>
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;

public void setDataSource(DataSource dataSource) {
    this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}

public int countOfActors(Actor exampleActor) {

    <lineannotation>// notice how the named parameters match the properties of the above '<classname>Actor</classname>' class</lineannotation>
    String sql = 
        "select count(*) from T_ACTOR where first_name = :firstName and last_name = :lastName";

    SqlParameterSource namedParameters = new BeanPropertySqlParameterSource(exampleActor);

    return this.namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}</programlisting>

      <para>Remember that the
      <classname>NamedParameterJdbcTemplate</classname> class
      <emphasis>wraps</emphasis> a classic <classname>JdbcTemplate</classname>
      template; if you need access to the wrapped
      <classname>JdbcTemplate</classname> instance to access functionality
      only present in the <classname>JdbcTemplate</classname> class, you can
      use the <methodname>getJdbcOperations()</methodname> method to access
      the wrapped <classname>JdbcTemplate</classname> through the
      <interfacename>JdbcOperations</interfacename> interface.</para>

      <para>See also <xref linkend="jdbc-JdbcTemplate-idioms" /> for
      guidelines on using the
      <classname>NamedParameterJdbcTemplate</classname> class in the context
      of an application.</para>
    </section>

    <section id="jdbc-SimpleJdbcTemplate">
      <title><classname>SimpleJdbcTemplate</classname></title>

      <para>The <classname>SimpleJdbcTemplate</classname> class wraps the
      classic <classname>JdbcTemplate</classname> and leverages Java 5
      language features such as varargs and autoboxing.</para>

      <note>
        <para>In Spring 3.0, the original <classname>JdbcTemplate</classname>
        also supports Java 5-enhanced syntax with generics and varargs.
        However, the <classname>SimpleJdbcTemplate</classname> provides a
        simpler API that works best when you do not need access to all the
        methods that the JdbcTemplate offers. Also, because the
        <classname>SimpleJdbcTemplate</classname> was designed for Java 5, it
        has more methods that take advantage of varargs due to different
        ordering of the parameters.</para>
      </note>

      <para>The value-add of the <classname>SimpleJdbcTemplate</classname>
      class in the area of syntactic-sugar is best illustrated with a
      before-and-after example. The next code snippet shows data access code
      that uses the classic <classname>JdbcTemplate</classname>, followed by a
      code snippet that does the same job with the
      <classname>SimpleJdbcTemplate</classname>.</para>

      <programlisting language="java"><lineannotation>// classic <classname>JdbcTemplate</classname>-style...</lineannotation>
private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {
    this.jdbcTemplate = new JdbcTemplate(dataSource);
}
<!--How is the code shown below different from the code shown in the next example? It seems like they're the same.-->
public Actor findActor(String specialty, int age) {

    String sql = "select id, first_name, last_name from T_ACTOR" + 
            " where specialty = ? and age = ?";
    
    RowMapper&lt;Actor&gt; mapper = new RowMapper&lt;Actor&gt;() {
        public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {
            Actor actor = new Actor();
            actor.setId(rs.getLong("id"));
            actor.setFirstName(rs.getString("first_name"));
            actor.setLastName(rs.getString("last_name"));
            return actor;
        }
    };

    
    <lineannotation>// notice the wrapping up of the argumenta in an array</lineannotation>
    return (Actor) jdbcTemplate.queryForObject(sql, new Object[] {specialty, age}, mapper);
}</programlisting>

      <para>Here is the same method, with the
      <classname>SimpleJdbcTemplate</classname>.<!--The code shown above is the same as the code shown below. What is the difference? 
TR: difference is in the way the parameters are passed in on the last line; no need to use an Objcet[].--></para>

      <programlisting language="java"><lineannotation>// <classname>SimpleJdbcTemplate</classname>-style...</lineannotation>
private SimpleJdbcTemplate simpleJdbcTemplate;

public void setDataSource(DataSource dataSource) {
    this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
}

public Actor findActor(String specialty, int age) {

    String sql = "select id, first_name, last_name from T_ACTOR" + 
            " where specialty = ? and age = ?";
    RowMapper&lt;Actor&gt; mapper = new RowMapper&lt;Actor&gt;() {  
        public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {
            Actor actor = new Actor();
            actor.setId(rs.getLong("id"));
            actor.setFirstName(rs.getString("first_name"));
            actor.setLastName(rs.getString("last_name"));
            return actor;
        }
    };

    <lineannotation>// notice the use of varargs since the parameter values now come 
    // after the RowMapper parameter</lineannotation>
    return this.simpleJdbcTemplate.queryForObject(sql, mapper, specialty, age);
}</programlisting>

      <para>See <xref linkend="jdbc-JdbcTemplate-idioms" /> for guidelines on
      how to use the <classname>SimpleJdbcTemplate</classname> class in the
      context of an application.</para>

      <note>
        <para>The <classname>SimpleJdbcTemplate</classname> class only offers
        a subset of the methods exposed on the
        <classname>JdbcTemplate</classname> class. If you need to use a method
        from the <classname>JdbcTemplate</classname> that is not defined on
        the <classname>SimpleJdbcTemplate</classname>, you can always access
        the underlying <classname>JdbcTemplate</classname> by calling the
        <methodname>getJdbcOperations()</methodname> method on the
        <classname>SimpleJdbcTemplate</classname>, which then allows you to
        invoke the method that you want. The only downside is that the methods
        on the <interfacename>JdbcOperations</interfacename> interface are not
        generic, so you are back to casting and so on.</para>
      </note>
    </section>

    <section id="jdbc-SQLExceptionTranslator">
      <title><interfacename>SQLExceptionTranslator</interfacename></title>

      <para><interfacename>SQLExceptionTranslator</interfacename> is an
      interface to be implemented by classes that can translate between
      <classname>SQLExceptions</classname> and Spring's own
      <classname>org.springframework.dao.DataAccessException</classname>,
      which is agnostic in regard to data access strategy. Implementations can
      be generic (for example, using SQLState codes for JDBC) or proprietary
      (for example, using Oracle error codes) for greater precision.</para>

      <para><classname>SQLErrorCodeSQLExceptionTranslator</classname> is the
      implementation of <interfacename>SQLExceptionTranslator</interfacename>
      that is used by default. This implementation uses specific vendor codes.
      It is more precise than the <literal>SQLState</literal> implementation.
      The error code translations are based on codes held in a JavaBean type
      class called <classname>SQLErrorCodes</classname>. This class is created
      and populated by an <classname>SQLErrorCodesFactory</classname> which as
      the name suggests is a factory for creating
      <classname>SQLErrorCodes</classname> based on the contents of a
      configuration file named <filename
      class="libraryfile">sql-error-codes.xml</filename>. This file is
      populated with vendor codes and based on the
      <code>DatabaseProductName</code> taken from the
      <interfacename>DatabaseMetaData</interfacename>. The codes for the acual
      database you are using are used.<!--what do you mean by *the current* database? --><!--TR: Revised, please review.--></para>

      <para>The <classname>SQLErrorCodeSQLExceptionTranslator</classname>
      applies matching rules in the following sequence: <!--This reflects sequence in which rules are applied, right? I revised to a numbered list.--><orderedlist
          spacing="compact">
          <note>
            <para>The <classname>SQLErrorCodesFactory</classname> is used by
            default to define Error codes and custom exception translations.
            They are looked up in a file named
            <filename>sql-error-codes.xml</filename> from the classpath and
            the matching <classname>SQLErrorCodes</classname> instance is
            located based on the database name from the database metadata of
            the database in use.</para>
          </note>

          <listitem>
            <para>Any custom translation implemented by a subclass. Normally
            the provided concrete
            <classname>SQLErrorCodeSQLExceptionTranslator</classname> is used
            so this rule does not apply. It only applies if you have actually
            provided a subclass implementation.<!--Pls revise last sentence to clarify. *Which* class is concrete? Why do you first refer to a subclass, then say *this class* is--><!--typically used and thus rule does not apply? This is really confusing.--><!--TR: Revised, please review.--></para>
          </listitem>

          <listitem>
            <para>Any custom implementation of the
            <classname>SQLExceptionTranslator</classname> interface that is
            provided as the
            <classname>customSqlExceptionTranslator</classname> property of
            the <classname>SQLErrorCodes</classname> class.</para>
          </listitem>

          <listitem>
            <para>The list of instances of the
            <classname>CustomSQLErrorCodesTranslation</classname> class,
            provided for the <classname>customTranslations</classname>
            property of the <classname>SQLErrorCodes</classname> class, are
            searched for a match.</para>
          </listitem>

          <listitem>
            <para>Error code matching is applied.<!--Wording of the next sentence does not track. Please revise. --><!--TR: Revised, please review.--></para>
          </listitem>

          <listitem>
            <para>Use the fallback translator.
            <classname>SQLExceptionSubclassTranslator</classname> is the
            default fallback translator. If this translation is not available
            then the next fallback translator is the
            <classname>SQLStateSQLExceptionTranslator</classname>.</para>
          </listitem>
        </orderedlist></para>

      <para>You can extend
      <classname>SQLErrorCodeSQLExceptionTranslator:</classname></para>

      <programlisting language="java">public class CustomSQLErrorCodesTranslator extends SQLErrorCodeSQLExceptionTranslator {

    protected DataAccessException customTranslate(String task, String sql, SQLException sqlex) {
        if (sqlex.getErrorCode() == -12345) {
            return new DeadlockLoserDataAccessException(task, sqlex);
        }
        return null;
    }
}</programlisting>

      <para>In this example, the specific error code <literal>-12345</literal>
      is translated and other errors are left to be translated by the default
      translator implementation. To use this custom translator, it is
      necessary to pass it to the <classname>JdbcTemplate</classname> through
      the method <literal>setExceptionTranslator</literal> and to use this
      <classname>JdbcTemplate</classname> for all of the data access
      processing where this translator is needed. Here is an example of how
      this custom translator can be used:</para>

      <programlisting language="java"><lineannotation>private JdbcTemplate jdbcTemoplate;

public void setDataSource(DataSource dataSource) {
    // create a <classname>JdbcTemplate</classname> and set data source</lineannotation> 
    this.jdbcTemplate = new JdbcTemplate(); 
    this.jdbcTemplate.setDataSource(dataSource); 
<lineannotation>    // create a custom translator and set the <interfacename>DataSource</interfacename> for the default translation lookup</lineannotation> 
    CustomSQLErrorCodesTranslator tr = new CustomSQLErrorCodesTranslator(); 
    tr.setDataSource(dataSource); 
    this.jdbcTemplate.setExceptionTranslator(tr); 
}

<lineannotation>public void updateShippingCharge(long orderId, long pct) {
    // use the <classname>prepared JdbcTemplate</classname> for this u<classname>pdate</classname></lineannotation>
    this.jdbcTemplate.update(
        "update orders" + 
            " set shipping_charge = shipping_charge * ? / 100" + 
            " where id = ?"
        pct, orderId); 
}</programlisting>

      <para>The custom translator is passed a data source in order to look up
      the error codes in <literal>sql-error-codes.xml</literal>.</para>
    </section>

    <section id="jdbc-statements-executing">
      <title>Executing statements</title>

      <para>Executing an SQL statement requires very little code. You need a
      <interfacename>DataSource</interfacename> and a
      <classname>JdbcTemplate</classname>, including the convenience
      methods<!--Does reader know what you mean by *convenience* methods? TR: OK as is. I hope they know what this is.-->
      that are provided with the <classname>JdbcTemplate</classname>. The
      following example shows what you need to include for a minimal but fully
      functional class that creates a new table:</para>

      <programlisting language="java">import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;

public class ExecuteAStatement {

    private JdbcTemplate jdbcTemplate;

    public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }

    public void doExecute() {
        this.jdbcTemplate.execute("create table mytable (id integer, name varchar(100))");
    }
}</programlisting>
    </section>

    <section id="jdbc-statements-querying">
      <title>Running queries</title>

      <para>Some query methods return a single value. To retrieve a count or a
      specific value from one row, use
      <methodname>queryForInt(..)</methodname>,
      <methodname>queryForLong(..)</methodname> or
      <methodname>queryForObject(..)</methodname>. The latter converts the
      returned JDBC <classname>Type</classname> to the Java class that is
      passed in as an argument. If the type conversion is invalid, then an
      <exceptionname>InvalidDataAccessApiUsageException</exceptionname> is
      thrown. Here is an example that contains two query methods, one for an
      <classname>int</classname> and one that queries for a
      <classname>String</classname>.</para>

      <programlisting language="java">import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;

public class RunAQuery {

    private JdbcTemplate jdbcTemplate;

    public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }
  
    public int getCount() {
        return this.jdbcTemplate.queryForInt("select count(*) from mytable");
    }

    public String getName() {
        return (String) this.jdbcTemplate.queryForObject("select name from mytable", String.class);
    }

    public void setDataSource(DataSource dataSource) {
        this.dataSource = dataSource;
    }
}</programlisting>

      <para>In addition to the single result query methods, several methods
      return a list with an entry for each row that the query returned. The
      most generic method is <methodname>queryForList(..)</methodname> which
      returns a <interfacename>List</interfacename> where each entry is a
      <interfacename>Map</interfacename> with each entry in the map
      representing the column value for that row. If you add a method to the
      above example to retrieve a list of all the rows, it would look like
      this:</para>

      <programlisting language="java">
private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {
    this.jdbcTemplate = new JdbcTemplate(dataSource);
}

public List&lt;Map&lt;String, Object&gt;&gt; getList() {
    return this.jdbcTemplate.queryForList("select * from mytable");
}</programlisting>

      <para>The list returned would look something like this:</para>

      <programlisting>[{name=Bob, id=1}, {name=Mary, id=2}]</programlisting>
    </section>

    <section id="jdbc-updates">
      <title>Updating the database</title>

      <para>The following example shows a column updated for a certain primary
      key. In this example, an SQL statement has placeholders for row
      parameters. The parameter values can be passed in as varargs or
      alternatively as an array of objects. Thus primitives should be wrapped
      in the primitive wrapper classes explicitly or using auto-boxing.</para>

      <programlisting language="java">import javax.sql.DataSource;

import org.springframework.jdbc.core.JdbcTemplate;

public class ExecuteAnUpdate {

    private JdbcTemplate jdbcTemplate;

    public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }

    public void setName(int id, String name) {
        this.jdbcTemplate.update(
                "update mytable set name = ? where id = ?", 
                name, id);
    }
}</programlisting>
    </section>

    <section id="jdbc-auto-genereted-keys">
      <title>Retrieving auto-generated keys</title>

      <para>An <methodname>update()</methodname> convenience method supports<!--Give name of this method. Also indicate *what* is acquiring the primary keys. TR: Changed to *retrieval*. 
The name of the method is *update*.--> the retrieval of primary keys generated
      by the database. This support is part of the JDBC 3.0 standard; see
      Chapter 13.6 of the specification for details. The method takes a
      <classname>PreparedStatementCreator</classname> as its first argument,
      and this is the way the required insert statement is specified. The
      other argument is a <classname>KeyHolder</classname>, which contains the
      generated key on successful return from the update. There is not a
      standard single way to create an appropriate
      <classname>PreparedStatement</classname> (which explains why the method
      signature is the way it is). The following example works on Oracle but
      may not work on other platforms:</para>

      <programlisting language="java">final String INSERT_SQL = "insert into my_test (name) values(?)";
final String name = "Rob";

KeyHolder keyHolder = new GeneratedKeyHolder();
jdbcTemplate.update(
    new PreparedStatementCreator() {
        public PreparedStatement createPreparedStatement(Connection connection) throws SQLException {
            PreparedStatement ps =
                connection.prepareStatement(INSERT_SQL, new String[] {"id"});
            ps.setString(1, name);
            return ps;
        }
    },
    keyHolder);

<lineannotation>// keyHolder.getKey() now contains the generated key</lineannotation></programlisting>
    </section>
  </section>

  <section id="jdbc-connections">
    <title>Controlling database connections</title>

    <section id="jdbc-datasource">
      <title><interfacename>DataSource</interfacename><!--I don't understand why *DataSource* was a subsection of *Using the JDBC classes to control basic JDBC processing and error handling*.--><!--According to *The package hierarchy*section, there is a datasource package, separate from the core package.So I moved it to this section. TR: OK.--></title>

      <para>Spring obtains a connection to the database through a
      <interfacename>DataSource</interfacename>. A
      <interfacename>DataSource</interfacename> is part of the JDBC
      specification and is a generalized connection factory. It allows a
      container or a framework to hide connection pooling and transaction
      management issues from the application code. As a developer, you need
      not know details about how to connect to the database; that is the
      responsibility of the administrator that sets up the datasource. You
      most likely fill both roles as you develop and test code, but you do not
      necessarily have to know how the production data source is
      configured.</para>

      <para>When using Spring's JDBC layer, you obtain a data source from JNDI
      or you configure your own with a connection pool implementation provided
      by a third party. Popular implementations are Apache Jakarta Commons
      DBCP and C3P0. Implementations in the Spring distribution are meant only
      for testing purposes and do not provide pooling.</para>

      <para>This section uses Spring's
      <classname>DriverManagerDataSource</classname> implementation, and
      several additional implementations are covered later.</para>

      <para><note>
          <para>Only use the <classname>DriverManagerDataSource</classname>
          class should only be used for testing purposes since it does not
          provide pooling and will perform poorly when multiple requests for a
          connection are made.</para>
        </note>You obtain a connection with
      <classname>DriverManagerDataSource</classname> as you typically obtain a
      JDBC connection. Specify the fully qualified classname of the JDBC
      driver so that the <classname>DriverManager</classname> can load the
      driver class. Next, provide a URL that varies between JDBC drivers.
      (Consult the documentation for your driver for the correct value.) Then
      provide a username and a password to connect to the database. Here is an
      example of how to configure a
      <classname>DriverManagerDataSource</classname> in Java code:</para>

      <programlisting language="java">DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName("org.hsqldb.jdbcDriver");
dataSource.setUrl("jdbc:hsqldb:hsql://localhost:");
dataSource.setUsername("sa");
dataSource.setPassword("");</programlisting>

      <para>Here is the corresponding XML configuration:</para>

      <programlisting language="java">&lt;bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"&gt;
    &lt;property name="driverClassName" value="${jdbc.driverClassName}"/&gt;
    &lt;property name="url" value="${jdbc.url}"/&gt;
    &lt;property name="username" value="${jdbc.username}"/&gt;
    &lt;property name="password" value="${jdbc.password}"/&gt;
&lt;/bean&gt;

&lt;context:property-placeholder location="jdbc.properties"/&gt;</programlisting>

      <para>The following examples show the basic connectivity and
      configuration for DBCP and C3P0. To learn about more options that help
      control the pooling features, see the product documentation for the
      respective connection pooling implementations.</para>

      <para>DBCP configuration:</para>

      <programlisting language="java">&lt;bean id="dataSource" 
        class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"&gt;
    &lt;property name="driverClassName" value="${jdbc.driverClassName}"/&gt;
    &lt;property name="url" value="${jdbc.url}"/&gt;
    &lt;property name="username" value="${jdbc.username}"/&gt;
    &lt;property name="password" value="${jdbc.password}"/&gt;
&lt;/bean&gt;

&lt;context:property-placeholder location="jdbc.properties"/&gt;</programlisting>

      <para>C3P0 configuration:</para>

      <programlisting language="java">&lt;bean id="dataSource"
        class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close"&gt;
    &lt;property name="driverClass" value="${jdbc.driverClassName}"/&gt;
    &lt;property name="jdbcUrl" value="${jdbc.url}"/&gt;
    &lt;property name="user" value="${jdbc.username}"/&gt;
    &lt;property name="password" value="${jdbc.password}"/&gt;
&lt;/bean&gt;

&lt;context:property-placeholder location="jdbc.properties"/&gt;</programlisting>
    </section>

    <section id="jdbc-DataSourceUtils">
      <title><classname>DataSourceUtils</classname></title>

      <para>The <classname>DataSourceUtils</classname> class is a convenient
      and powerful helper class that provides <literal>static</literal>
      methods to obtain connections from JNDI and close connections if
      necessary. It supports thread-bound connections with, for example,
      <classname>DataSourceTransactionManager</classname>.</para>
    </section>

    <section id="jdbc-SmartDataSource">
      <title><interfacename>SmartDataSource</interfacename></title>

      <para>The <interfacename>SmartDataSource</interfacename> interface
      should be implemented by classes that can provide a connection to a
      relational database. It extends the
      <interfacename>DataSource</interfacename> interface to allow classes
      using it to query whether the connection should be closed after a given
      operation. This usage is efficient when you know that you will reuse a
      connection.</para>
    </section>

    <section id="jdbc-AbstractDataSource">
      <title><classname>AbstractDataSource</classname></title>

      <para><code><classname>AbstractDataSource</classname></code> is an
      <literal><classname>abstract</classname></literal> base class for
      Spring's <interfacename>DataSource</interfacename> implementations that
      implements code that is common to all <classname>DataSource</classname>
      implementations.<!--Please revise *takes care of uninteresting glue* to specify what exactly it does. Avoid slang and idomatic language, --><!--especially important with non-native English readers. TR: Revised, please review.-->
      You extend the <classname>AbstractDataSource</classname> class if you
      are writing your own <interfacename>DataSource</interfacename>
      implementation.<!--Preceding revision ok? If not, revise to specify *which* class you extend if you are writing your own DataSource imp. TR: OK.--></para>
    </section>

    <section id="jdbc-SingleConnectionDataSource">
      <title><classname>SingleConnectionDataSource</classname></title>

      <para>The <classname>SingleConnectionDataSource</classname> class is an
      implementation of the <interfacename>SmartDataSource</interfacename>
      interface that wraps a <emphasis>single</emphasis>
      <interfacename>Connection</interfacename> that is
      <emphasis>not</emphasis> closed after each use. Obviously, this is not
      multi-threading capable.</para>

      <para>If any client code calls <command>close</command> in the
      assumption of a pooled connection, as when using persistence tools, set
      the <literal>suppressClose</literal> property to
      <literal>true</literal>. <!--Have I revised this correctly? THe client code is calling *close*? If not, revise to clarify. Also WHERE do you set --><!--suppressClose to true? TR: OK. suppressClose is set directly on the SingleConnectionDataSource instance.-->This
      setting returns a close-suppressing proxy wrapping the physical
      connection. Be aware that you will not be able to cast this<!--this *what*?-->
      to a native Oracle <interfacename>Connection</interfacename> or the like
      anymore.</para>

      <para>This is primarily a test class. For example, it enables easy
      testing of code outside an application server, in conjunction with a
      simple JNDI environment. In contrast to
      <classname>DriverManagerDataSource</classname>, it reuses the same
      connection all the time, avoiding excessive creation of physical
      connections.</para>
    </section>

    <section id="jdbc-DriverManagerDataSource">
      <title><classname>DriverManagerDataSource</classname></title>

      <para>The <classname>DriverManagerDataSource</classname> class is an
      implementation of the standard <interfacename>DataSource</interfacename>
      interface that configures a plain JDBC driver through bean properties,
      and returns a new <interfacename>Connection</interfacename> every
      time.</para>

      <para>This implementation is useful for test and stand-alone
      environments outside of a Java EE container, either as a
      <interfacename>DataSource</interfacename> bean in a Spring IoC
      container, or in conjunction with a simple JNDI environment.
      Pool-assuming <literal>Connection.close()</literal> calls will simply
      close the connection, so any
      <interfacename>DataSource</interfacename>-aware persistence code should
      work. However, using JavaBean-style connection pools such as
      <code>commons-dbcp</code> is so easy, even in a test environment, that
      it is almost always preferable to use such a connection pool over
      <classname>DriverManagerDataSource</classname>.</para>
    </section>

    <section id="jdbc-TransactionAwareDataSourceProxy">
      <title><classname>TransactionAwareDataSourceProxy</classname></title>

      <para><classname>TransactionAwareDataSourceProxy</classname> is a proxy
      for a target <interfacename>DataSource</interfacename>, which wraps that
      target <interfacename>DataSource</interfacename> to add awareness of
      Spring-managed transactions. In this respect, it is similar to a
      transactional JNDI <interfacename>DataSource</interfacename> as provided
      by a Java EE server.</para>

      <note>
        <para>It is rarely desirable to use this class, except when already
        existing code that must be called and passed a standard JDBC
        <interfacename>DataSource</interfacename> interface implementation. In
        this case, it's possible to still have this code be usable, and at the
        same time have this code participating in Spring managed transactions.
        <!--Clarify preceding sentence. Are you saying, if you use TransactionAwareDataSource Proxy in this case, then what?--><!--I don't get the *usable, but* participating in Spring-managed transactions. TR: Revised, please review. -->It
        is generally preferable to write your own new code using the higher
        level abstractions for resource management, such as
        <classname>JdbcTemplate</classname> or
        <classname>DataSourceUtils</classname>.</para>
      </note>

      <para><emphasis>(See the
      <classname>TransactionAwareDataSourceProxy</classname> Javadocs for more
      details.)</emphasis></para>
    </section>

    <section id="jdbc-DataSourceTransactionManager">
      <title><classname>DataSourceTransactionManager</classname></title>

      <para>The <classname>DataSourceTransactionManager</classname> class is a
      <interfacename>PlatformTransactionManager</interfacename> implementation
      for single JDBC datasources. It binds a JDBC connection from the
      specified data source to the currently executing thread, potentially
      allowing for one thread connection per data source.</para>

      <para>Application code is required <!--app code such as what, for example? What do you have to provide? TR: OK as is.-->to
      retrieve the JDBC connection through
      <literal>DataSourceUtils.getConnection(DataSource)</literal> instead of
      Java EE's standard <literal>DataSource.getConnection</literal>. It
      throws unchecked <literal>org.springframework.dao</literal> exceptions
      instead of checked <exceptionname>SQLExceptions</exceptionname>. All
      framework classes like <classname>JdbcTemplate</classname> use this
      strategy implicitly. If not used with this transaction manager, the
      lookup strategy behaves exactly like the common one - it can thus be
      used in any case.</para>

      <para>The <classname>DataSourceTransactionManager</classname> class
      supports custom isolation levels, and timeouts that get applied as
      appropriate JDBC statement query timeouts. To support the latter,
      application code must either use <classname>JdbcTemplate</classname> or
      call the <literal>DataSourceUtils.applyTransactionTimeout(..)</literal>
      method for each created statement.</para>

      <para>This implementation can be used instead of
      <classname>JtaTransactionManager</classname> in the single resource
      case, as it does not require the container to support JTA. Switching
      between both is just a matter of configuration, if you stick to the
      required connection lookup pattern. JTA does not support custom
      isolation levels!</para>
    </section>

    <section id="jdbc-NativeJdbcExtractor">
      <title>NativeJdbcExtractor</title>

      <para>Sometimes you need to access vendor specific JDBC methods that
      differ from the standard JDBC API. This can be problematic if you are
      running in an application server or with a
      <classname>DataSource</classname> that wraps the
      <classname>Connection</classname>, <classname>Statement</classname> and
      <classname>ResultSet</classname> objects with its own wrapper objects.
      To gain access to the native objects you can configure your
      <classname>JdbcTemplate</classname> or
      <classname>OracleLobHandler</classname> with a
      <classname>NativeJdbcExtractor</classname>.</para>

      <para>The <code>NativeJdbcExtractor</code> comes in a variety of flavors
      to match your execution environment:</para>

      <itemizedlist>
        <listitem>
          <para>SimpleNativeJdbcExtractor</para>
        </listitem>

        <listitem>
          <para>C3P0NativeJdbcExtractor</para>
        </listitem>

        <listitem>
          <para>CommonsDbcpNativeJdbcExtractor</para>
        </listitem>

        <listitem>
          <para>JBossNativeJdbcExtractor</para>
        </listitem>

        <listitem>
          <para>WebLogicNativeJdbcExtractor</para>
        </listitem>

        <listitem>
          <para>WebSphereNativeJdbcExtractor</para>
        </listitem>

        <listitem>
          <para>XAPoolNativeJdbcExtractor</para>
        </listitem>
      </itemizedlist>

      <para>Usually the <classname>SimpleNativeJdbcExtractor</classname> is
      sufficient for unwrapping a <classname>Connection</classname> object in
      most environments. See the Javadocs for more details.</para>
    </section>
  </section>

  <section id="jdbc-advanced-jdbc">
    <title>JDBC batch operations</title>

    <para>Most JDBC drivers provide improved performance if you batch multiple
    calls to the same prepared statement. By grouping updates into batches you
    limit the number of round trips to the database. This section covers batch
    processing using both the <classname>JdbcTemplate</classname> and the
    <classname>SimpleJdbcTemplate</classname>.</para>

    <section id="jdbc-advanced-classic">
      <title>Batch operations with the JdbcTemplate</title>

      <para>You accomplish <classname>JdbcTemplate</classname> batch
      processing by implementing two methods of a special interface,
      <classname>BatchPreparedStatementSetter</classname>, and passing that in
      as the second parameter in your <classname>batchUpdate</classname>
      method call. Use the <classname>getBatchSize</classname> method to
      provide the size of the current batch. Use the
      <classname>setValues</classname> method to set the values for the
      parameters of the prepared statement. This method will be called the
      number of times that you specified in the
      <classname>getBatchSize</classname> call. The following example updates
      the actor table based on entries in a list. The entire list is used as
      the batch in this example:</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private JdbcTemplate jdbcTemplate;

    public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }

    public int[] batchUpdate(final List&lt;Actor&gt; actors) {
        int[] updateCounts = jdbcTemplate.batchUpdate(
                "update t_actor set first_name = ?, last_name = ? where id = ?",
                new BatchPreparedStatementSetter() {
                    public void setValues(PreparedStatement ps, int i) throws SQLException {
                        ps.setString(1, actors.get(i).getFirstName());
                        ps.setString(2, actors.get(i).getLastName());
                        ps.setLong(3, actors.get(i).getId().longValue());
                    }

                    public int getBatchSize() {
                        return actors.size();
                    }
                } );
        return updateCounts;
    }

    //  ... additional methods
}</programlisting>If you are processing a stream of updates or reading from a
      file, then you might have a preferred batch size, but the last batch
      might not have that number of entries. In this case you can use the
      <classname>InterruptibleBatchPreparedStatementSetter</classname>
      interface, which allows you to interrupt a batch once the input source
      is exhausted. The <classname>isBatchExhausted</classname> method allows
      you to signal the end of the batch.</para>
    </section>

    <section id="jdbc-advanced-simple">
      <title>Batch operations with the SimpleJdbcTemplate</title>

      <para>The <classname>SimpleJdbcTemplate</classname> provides an
      alternate way of providing the batch update. Instead of implementing a
      special batch interface, you provide all parameter values in the call.
      The framework loops over these values and uses an internal prepared
      statement setter. The API varies depending on whether you use named
      parameters. For the named parameters you provide an array of
      <classname>SqlParameterSource</classname>, one entry for each member of
      the batch. You can use the
      <classname>SqlParameterSource.createBatch</classname> method to create
      this array, passing in either an array of JavaBeans or an array of Maps
      containing the parameter values.</para>

      <para>This example shows a batch update using named parameters:</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
    }

    public int[] batchUpdate(final List&lt;Actor&gt; actors) {
        SqlParameterSource[] batch = SqlParameterSourceUtils.createBatch(actors.toArray());
        int[] updateCounts = simpleJdbcTemplate.batchUpdate(
            "update t_actor set first_name = :firstName, last_name = :lastName where id = :id",
            batch);
        return updateCounts;
    }

    //  ... additional methods
}</programlisting>For an SQL statement using the classic "?" placeholders, you
      pass in a list containing an object array with the update values. This
      object array must have one entry for each placeholder in the SQL
      statement, and they must be in the same order as they are defined in the
      SQL statement.</para>

      <para>The same example using classic JDBC "?" placeholders:</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
    }

    public int[] batchUpdate(final List&lt;Actor&gt; actors) {
        List&lt;Object[]&gt; batch = new ArrayList&lt;Object[]&gt;();
        for (Actor actor : actors) {
            Object[] values = new Object[] {
                    actor.getFirstName(),
                    actor.getLastName(),
                    actor.getId()};
            batch.add(values);
        }
        int[] updateCounts = simpleJdbcTemplate.batchUpdate(
                "update t_actor set first_name = ?, last_name = ? where id = ?",
                batch);
        return updateCounts;
    }

    //  ... additional methods
}</programlisting>All batch update methods return an int array containing the
      number of affected rows for each batch entry. This count is reported by
      the JDBC driver. If the count is not available, the JDBC driver returns
      a -2 value.</para>
    </section>
  </section>

  <section id="jdbc-simple-jdbc">
    <title>Simplifying JDBC operations with the SimpleJdbc classes</title>

    <para>The <classname>SimpleJdbcInsert</classname> and
    <classname>SimpleJdbcCall</classname> classes provide a simplified
    configuration by taking advantage of database metadata that can be
    retrieved through the JDBC driver. This means there is less to configure
    up front, although you can override or turn off the metadata processing if
    you prefer to provide all the details in your code.</para>

    <section id="jdbc-simple-jdbc-insert-1">
      <title>Inserting data using SimpleJdbcInsert</title>

      <para>Let's start by looking at the
      <classname>SimpleJdbcInsert</classname> class with the minimal amount of
      configuration options. You should instantiate the
      <classname>SimpleJdbcInsert</classname> in the data access layer's
      initialization method. <!--What do you mean *should be*? Are you saying a human should do it. If so, say *You should instantiate the SimpleJdbcInsert...* Also, is--><!--it correct to say *in* the data access layer's init method? Should it be *with*. Below, what do you mean by *fluid style*? 
TR: Revised, please review.-->For this example, the initializing method is the
      <classname>setDataSource</classname> method. You do not need to subclass
      the <classname>SimpleJdbcInsert</classname> class; simply create a new
      instance and set the table name using the
      <classname>withTableName</classname> method. Configuration methods for
      this class follow the "fluid" style that returns the instance of the
      <classname>SimpleJdbcInsert</classname>, which allows you to chain all
      configuration methods. This example uses only one configuration method;
      you will see examples of multiple ones later.</para>

      <programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private SimpleJdbcInsert insertActor;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        this.insertActor = 
                new SimpleJdbcInsert(dataSource).withTableName("t_actor");
    }

    public void add(Actor actor) {
        Map&lt;String, Object&gt; parameters = new HashMap&lt;String, Object&gt;(3);
        parameters.put("id", actor.getId());
        parameters.put("first_name", actor.getFirstName());
        parameters.put("last_name", actor.getLastName());
        insertActor.execute(parameters);
    }

    //  ... additional methods
}</programlisting>

      <para>The execute method used here takes a plain
      <classname>java.utils.Map</classname> as its only parameter. The
      important thing to note here is that the keys used for the Map must
      match the column names of the table as defined in the database. This is
      because we read the metadata in order to construct the actual insert
      statement.</para>
    </section>

    <section id="jdbc-simple-jdbc-insert-2">
      <title>Retrieving auto-generated keys using SimpleJdbcInsert</title>

      <para>This example uses the same insert as the preceding, but instead of
      passing in the id it retrieves the auto-generated key and sets it on the
      new Actor object. When you create the
      <classname>SimpleJdbcInsert</classname>, in addition to specifying the
      table name, you specify the name of the generated key column with the
      <classname>usingGeneratedKeyColumns</classname> method.</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private SimpleJdbcInsert insertActor;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        this.insertActor =
                new SimpleJdbcInsert(dataSource)
                        .withTableName("t_actor")
                        .usingGeneratedKeyColumns("id");
    }

    public void add(Actor actor) {
        Map&lt;String, Object&gt; parameters = new HashMap&lt;String, Object&gt;(2);
        parameters.put("first_name", actor.getFirstName());
        parameters.put("last_name", actor.getLastName());
        Number newId = insertActor.executeAndReturnKey(parameters);
        actor.setId(newId.longValue());
    }

    //  ... additional methods
}</programlisting>The main difference when executing the insert by this second
      approach is that you do not add the id to the Map and you call the
      <literal>executeReturningKey</literal> method. This returns a
      <literal>java.lang.Number</literal> object with which you can create an
      instance of the numerical type that is used in our domain class.You
      cannot rely on all databases to return a specific Java class here;
      <literal>java.lang.Number</literal> is the base class that you can rely
      on. If you have multiple auto-generated columns, or the generated values
      are non-numeric, then you can use a <literal>KeyHolder</literal> that is
      returned from the <literal>executeReturningKeyHolder</literal>
      method.</para>
    </section>

    <section id="jdbc-simple-jdbc-insert-3">
      <title>Specifying columns for a SimpleJdbcInsert</title>

      <para>You can limit the columns for an insert by specifying a list of
      column names with the <classname>usingColumns</classname> method:</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private SimpleJdbcInsert insertActor;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        this.insertActor =
                new SimpleJdbcInsert(dataSource)
                        .withTableName("t_actor")
                        .usingColumns("first_name", "last_name")
                        .usingGeneratedKeyColumns("id");
    }

    public void add(Actor actor) {
        Map&lt;String, Object&gt; parameters = new HashMap&lt;String, Object&gt;(2);
        parameters.put("first_name", actor.getFirstName());
        parameters.put("last_name", actor.getLastName());
        Number newId = insertActor.executeAndReturnKey(parameters);
        actor.setId(newId.longValue());
    }

    //  ... additional methods
}</programlisting>The execution of the insert is the same as if you had relied
      on the metadata to determine which columns to use.</para>
    </section>

    <section id="jdbc-simple-jdbc-parameters">
      <title>Using SqlParameterSource to provide parameter values</title>

      <para>Using a <classname>Map</classname> to provide parameter values
      works fine, but it's not the most convenient class to use. Spring
      provides a couple of implementations of the
      <classname>SqlParameterSource</classname> interface that can be used
      instead.<!--But *what* class (classname?) is not the most convenient? TR: OK as is.-->The
      first one is <classname>BeanPropertySqlParameterSource</classname>,
      which is a very convenient class if you have a JavaBean-compliant class
      that contains your values. It will use the corresponding getter method
      to extract the parameter values. Here is an example:</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private SimpleJdbcInsert insertActor;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        this.insertActor =
                new SimpleJdbcInsert(dataSource)
                        .withTableName("t_actor")
                        .usingGeneratedKeyColumns("id");
    }

    public void add(Actor actor) {
        SqlParameterSource parameters = new BeanPropertySqlParameterSource(actor);
        Number newId = insertActor.executeAndReturnKey(parameters);
        actor.setId(newId.longValue());
    }

    //  ... additional methods
}</programlisting>Another option is the
      <classname>MapSqlParameterSource</classname> that resembles a Map but
      provides a more convenient <classname>addValue</classname> method that
      can be chained.</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private SimpleJdbcInsert insertActor;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        this.insertActor =
                new SimpleJdbcInsert(dataSource)
                        .withTableName("t_actor")
                        .usingGeneratedKeyColumns("id");
    }

    public void add(Actor actor) {
        SqlParameterSource parameters = new MapSqlParameterSource()
                .addValue("first_name", actor.getFirstName())
                .addValue("last_name", actor.getLastName());
        Number newId = insertActor.executeAndReturnKey(parameters);
        actor.setId(newId.longValue());
    }

    //  ... additional methods
}</programlisting>As you can see, the configuration is the same; only the
      executing code has to change to use these alternative input
      classes.</para>
    </section>

    <section id="jdbc-simple-jdbc-call-1">
      <title>Calling a stored procedure with SimpleJdbcCall</title>

      <para>The <classname>SimpleJdbcCall</classname> class leverages metadata
      in the database to look up names of <code>in</code> and <code>out</code>
      parameters, so that you do not have to declare them explicitly. You can
      declare parameters if you prefer to do that, or if you have parameters
      such as <code>ARRAY</code> or <code>STRUCT</code> that do not have an
      automatic mapping to a Java class. The first example shows a simple
      procedure that returns only scalar values in <code>VARCHAR</code> and
      <code>DATE</code> format from a MySQL database. The example procedure
      reads a specified actor entry and returns <code>first_name</code>,
      <code>last_name</code>, and <code>birth_date</code> columns in the form
      of <code>out</code> parameters.</para>

      <para><programlisting>CREATE PROCEDURE read_actor ( 
  IN in_id INTEGER, 
  OUT out_first_name VARCHAR(100), 
  OUT out_last_name VARCHAR(100), 
  OUT out_birth_date DATE) 
BEGIN 
  SELECT first_name, last_name, birth_date 
  INTO out_first_name, out_last_name, out_birth_date 
  FROM t_actor where id = in_id;
END;</programlisting>The <code>in_id</code> parameter contains the
      <code>id</code> of the actor you are looking up. The <code>out</code>
      parameters return the data read from the table.</para>

      <para>The <classname>SimpleJdbcCall</classname> is declared in a similar
      manner to the <classname>SimpleJdbcInsert</classname>. You should
      instantiate and configure the class in the initialization method of your
      data access layer. Compared to the StoredProcedure class, you don't
      have to create a subclass and you don't have to declare parameters that
      can be looked up in the database metadata. <!--Reword preceding: You need not subclass *what?* and you declare *what* in init method? TR: Revised, pplease review.-->Following
      is an example of a SimpleJdbcCall configuration using the above stored
      procedure. The only configuration option, in addition to the
      <classname>DataSource</classname>, is the name of the stored
      procedure.<!--Indicate what the purpose of this example is (what it does) and identify the name of procedure. Also see next query. TR: Revised, please review.--></para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private SimpleJdbcCall procReadActor;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        this.procReadActor =
                new SimpleJdbcCall(dataSource)
                        .withProcedureName("read_actor");
    }

    public Actor readActor(Long id) {
        SqlParameterSource in = new MapSqlParameterSource()
                .addValue("in_id", id); 
        Map out = procReadActor.execute(in);
        Actor actor = new Actor();
        actor.setId(id);
        actor.setFirstName((String) out.get("out_first_name"));
        actor.setLastName((String) out.get("out_last_name"));
        actor.setBirthDate((Date) out.get("out_birth_date"));
        return actor;
    }

    //  ... additional methods
}</programlisting>The code you write for the execution of the call involves
      creating an <classname>SqlParameterSource</classname> containing the IN
      parameter. <!--sentence before this one said *all you need to specify* is name of procedure, but preceding sentence says it involves creating an--><!--SQLParameterSource. Isn't this *in addition* to specifying procedure name? Revise to clarify what a human does in this example. --><!--Reword preceding to clarify whether a human creates the SqlParameterSource. 
TR: Revised, please review. Execution is separate from declaration, so we still only need to declare the name of the proc.-->It's
      important to match the name provided for the input value with that of
      the parameter name <!--match *what* to the name of parameter in stored procedure?? And if this is something you're telling a human to do,--><!--reword to say *You must match <what> to the name of the parameter etc* TR: Revised.-->declared
      in the stored procedure. The case does not have to match because you use
      metadata to determine how database objects should be referred to in a
      stored procedure. What is specified in the source for the stored
      procedure is not necessarily the way it is stored in the database. Some
      databases transform names to all upper case while others use lower case
      or use the case as specified.</para>

      <para>The <classname>execute</classname> method takes the IN parameters
      and returns a Map containing any <code>out</code> parameters keyed by
      the name as specified in the stored procedure. In this case they are
      <classname>out_first_name, out_last_name</classname> and
      <classname>out_birth_date</classname>.</para>

      <para>The last part of the <classname>execute</classname> method creates
      an Actor instance to use to return the data retrieved. Again, it is
      important to use the names of the <code>out</code> parameters as they
      are declared in the stored procedure. <!--*match* them how? What are you matching to what? I see three different out parameters (first name, last name, birth date). Revise. TR: Revised.-->Also,
      the case in the names of the <code>out</code> parameters stored in the
      results map matches that of the <code>out</code> parameter names in the
      database, which could vary between databases. <!--Preceding sentence, are you saying the case will match, or it *should*? Next sentence, state why you are doing what you are told to do. TR: Revised.-->To
      make your code more portable you should do a case-insensitive lookup or
      instruct Spring to use a <classname>CaseInsensitiveMap</classname> from
      the Jakarta Commons project. To do the latter, you create your own
      <classname>JdbcTemplate</classname> and set the
      <classname>setResultsMapCaseInsensitive</classname> property to
      <classname>true</classname>. Then you pass this customized
      <classname>JdbcTemplate</classname> instance into the constructor of
      your <classname>SimpleJdbcCall</classname>. You must include the
      <classname>commons-collections.jar</classname> in your classpath for
      this to work. Here is an example of this configuration:</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcCall procReadActor;

    public void setDataSource(DataSource dataSource) {
        JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
        jdbcTemplate.setResultsMapCaseInsensitive(true);
        this.procReadActor =
                new SimpleJdbcCall(jdbcTemplate)
                        .withProcedureName("read_actor");
    }


    //  ... additional methods
}</programlisting>By taking this action, you avoid conflicts in the case used
      for the names of your returned <code>out</code> parameters.</para>
    </section>

    <section id="jdbc-simple-jdbc-call-2">
      <title>Explicitly declaring parameters to use for a
      SimpleJdbcCall</title>

      <para>You have seen how the parameters are deduced based on metadata,
      but you can declare then explicitly if you wish. You do this by creating
      and configuring <classname>SimpleJdbcCall</classname> with the
      <classname>declareParameters</classname> method, which takes a variable
      number of <classname>SqlParameter</classname> objects as input. See the
      next section for details on how to define an
      <classname>SqlParameter</classname>.<!--Moved following info from end of section and made it a note. Important to know this up front. TR: OK.--></para>

      <para><note>
          <para>Explicit declarations are necessary if the database you use is
          not a Spring-supported database. Currently Spring supports metadata
          lookup of stored procedure calls for the following databases: Apache
          Derby, DB2, MySQL, Microsoft SQL Server, Oracle, and Sybase. We also
          support metadata lookup of stored functions for: MySQL, Microsoft
          SQL Server, and Oracle.</para>
        </note></para>

      <para>You can opt to declare one, some, or all the parameters
      explicitly. The parameter metadata is still used where you do not
      declare parameters explicitly. <!--Is my rewording of preceding sentence ok? (See next sentence.)-->To
      bypass all processing of metadata lookups for potential parameters and
      only use the declared parameters, you call the method
      <classname>withoutProcedureColumnMetaDataAccess</classname> as part of
      the declaration. Suppose that you have two or more different call
      signatures declared for a database function. In this case you call the
      <classname>useInParameterNames</classname> to specify the list of IN
      parameter names to include for a given signature.</para>

      <para>The following example shows a fully declared procedure call, using
      the information from the preceding example.</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcCall procReadActor;

    public void setDataSource(DataSource dataSource) {
        JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
        jdbcTemplate.setResultsMapCaseInsensitive(true);
        this.procReadActor =
                new SimpleJdbcCall(jdbcTemplate)
                        .withProcedureName("read_actor")
                        .withoutProcedureColumnMetaDataAccess()
                        .useInParameterNames("in_id")
                        .declareParameters(
                                new SqlParameter("in_id", Types.NUMERIC),
                                new SqlOutParameter("out_first_name", Types.VARCHAR),
                                new SqlOutParameter("out_last_name", Types.VARCHAR),
                                new SqlOutParameter("out_birth_date", Types.DATE)
                        );
    }


    //  ... additional methods
}</programlisting>The execution and end results of the two examples are the
      same; this one specifies all details explicitly rather than relying on
      metadata.</para>
    </section>

    <section id="jdbc-params">
      <title>How to define SqlParameters</title>

      <para>To define a parameter for the SimpleJdbc classes and also for the
      RDBMS operations classes, covered in <xref linkend="jdbc-object" />,
      <!--Deleted *described in following section* because RDBMS not mentioned in next section (5.8). Revise to give link to section you mean.-->you
      use an <classname>SqlParameter</classname> or one of its subclasses. You
      typically specify the parameter name and SQL type in the constructor.
      The SQL type is specified using the
      <classname>java.sql.Types</classname> constants. We have already seen
      declarations like:</para>

      <para><programlisting language="java">   new SqlParameter("in_id", Types.NUMERIC),
   new SqlOutParameter("out_first_name", Types.VARCHAR),</programlisting></para>

      <para>The first line with the <classname>SqlParameter</classname>
      declares an IN parameter. IN parameters can be used for both stored
      procedure calls and for queries using the
      <classname>SqlQuery</classname> and its subclasses covered in the
      following section.</para>

      <para>The second line with the <classname>SqlOutParameter</classname>
      declares an <code>out</code> parameter to be used in a stored procedure
      call. There is also an <classname>SqlInOutParameter</classname> for
      <code>InOut</code> parameters, parameters that provide an
      <code>IN</code> value to the procedure and that also return a
      value.</para>

      <note>
        <para>Only parameters declared as <classname>SqlParameter</classname>
        and <classname>SqlInOutParameter</classname> will be used to provide
        input values. This is different from the
        <classname>StoredProcedure</classname> class, which for backwards
        compatibility reasons allows input values to be provided for
        parameters declared as <classname>SqlOutParameter</classname>.</para>
      </note>

      <para>For IN parameters, in addition to the name and the SQL type, you
      can specify a scale for numeric data or a type name for custom database
      types. For <code>out</code> parameters, you can provide a
      <classname>RowMapper</classname> to handle mapping of rows returned from
      a <code>REF</code> cursor. Another option is to specify an
      <classname>SqlReturnType</classname> that provides an opportunity to
      define customized handling of the return values.</para>
    </section>

    <section id="jdbc-simple-jdbc-call-3">
      <title>Calling a stored function using SimpleJdbcCall</title>

      <para>You call a stored function in almost the same way as you call a
      stored procedure, except that you provide a function name rather than a
      procedure name. You use the <classname>withFunctionName</classname>
      method as part of the configuration to indicate that we want to make a
      call to a function, and the corresponding string for a function call is
      generated. A specialized execute call,
      <classname>executeFunction,</classname> is used to execute the function
      and it returns the function return value as an object of a specified
      type, which means you do not have to retrieve the return value from the
      results map. <!--Are you saying you use withFunctionName, *then* use executeFunction? OR do you use one *or* the other? revise to clarify. Second --><!--snippet below uses both. TR: Revised.-->A
      similar convenience method named <classname>executeObject</classname> is
      also available for stored procedures that only have one <code>out</code>
      parameter. The following example is based on a stored function named
      <classname>get_actor_name</classname> that returns an actor's full name.
      Here is the MySQL source for this function:</para>

      <para><programlisting>CREATE FUNCTION get_actor_name (in_id INTEGER)
RETURNS VARCHAR(200) READS SQL DATA 
BEGIN
  DECLARE out_name VARCHAR(200);
  SELECT concat(first_name, ' ', last_name)
    INTO out_name
    FROM t_actor where id = in_id;
  RETURN out_name;
END;</programlisting></para>

      <para>To call this function we again create a
      <classname>SimpleJdbcCall</classname> in the initialization
      method.</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private SimpleJdbcCall funcGetActorName;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
        jdbcTemplate.setResultsMapCaseInsensitive(true);
        this.funcGetActorName =
                new SimpleJdbcCall(jdbcTemplate)
                        .withFunctionName("get_actor_name");
    }

    public String getActorName(Long id) {
        SqlParameterSource in = new MapSqlParameterSource()
                .addValue("in_id", id); 
        String name = funcGetActorName.executeFunction(String.class, in);
        return name;
    }

    //  ... additional methods
}</programlisting>The execute method <!--In paragraph before first example it refers to executeFunction; is this what you mean by execute method? TR: Yes.-->used
      returns a <classname>String</classname> containing the return value from
      the function call.</para>
    </section>

    <section id="jdbc-simple-jdbc-call-4">
      <title>Returning ResultSet/REF Cursor from a SimpleJdbcCall</title>

      <para>Calling a stored procedure or function that returns a result set
      is a bit tricky. Some databases return result sets during the JDBC
      results processing while others require an explicitly registered
      <code>out</code> parameter of a specific type. Both approaches need
      additional processing to loop over the result set and process the
      returned rows. With the <classname>SimpleJdbcCall</classname> you use
      the <classname>returningResultSet</classname> method and declare a
      <classname>RowMapper</classname> implementation to be used for a
      specific parameter. In the case where the result set is returned during
      the results processing, there are no names defined, so the returned
      results will have to match the order in which you declare the
      <classname>RowMapper</classname> implementations. The name specified is
      still used to store the processed list of results in the results map
      that is returned from the execute statement.</para>

      <para>The next example uses a stored procedure that takes no IN
      parameters and returns all rows from the t_actor table. Here is the
      MySQL source for this procedure:</para>

      <para><programlisting>CREATE PROCEDURE read_all_actors()
BEGIN
 SELECT a.id, a.first_name, a.last_name, a.birth_date FROM t_actor a;
END;</programlisting>To call this procedure you declare the
      <classname>RowMapper</classname>. Because the class you want to map to
      follows the JavaBean rules, you can use a
      <classname>ParameterizedBeanPropertyRowMapper</classname> that is
      created by passing in the required class to map to in the
      <classname>newInstance</classname> method.</para>

      <para><programlisting language="java">public class JdbcActorDao implements ActorDao {
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private SimpleJdbcCall procReadAllActors;

    public void setDataSource(DataSource dataSource) {
        this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
        jdbcTemplate.setResultsMapCaseInsensitive(true);
        this.procReadAllActors =
                new SimpleJdbcCall(jdbcTemplate)
                        .withProcedureName("read_all_actors")
                        .returningResultSet("actors",
                                ParameterizedBeanPropertyRowMapper.newInstance(Actor.class));
    }

    public List getActorsList() {
        Map m = procReadAllActors.execute(new HashMap&lt;String, Object&gt;(0));
        return (List) m.get("actors");
    }

    //  ... additional methods
}</programlisting>The execute call passes in an empty Map because this call
      does not take any parameters. The list of Actors is then retrieved from
      the results map and returned to the caller.</para>
    </section>
  </section>

  <section id="jdbc-object">
    <title>Modeling JDBC operations as Java objects</title>

    <para>The <literal>org.springframework.jdbc.object</literal> package
    contains classes that allow you to access the database in a more
    object-oriented manner. As an example, you can execute queries and get the
    results back as a list containing business objects with the relational
    column data mapped to the properties of the business object. You can also
    execute stored procedures and run update, delete, and insert
    statements.</para>

    <note>
      <para>Many Spring developers believe that the various RDBMS operation
      classes described below (with the exception of the <link
      linkend="jdbc-StoredProcedure"><classname>StoredProcedure</classname></link>
      class) can often be replaced with straight
      <classname>JdbcTemplate</classname> calls. Often it is simpler to write
      a DAO method that simply calls a method on a
      <classname>JdbcTemplate</classname> directly (as opposed to
      encapsulating a query as a full-blown class).<!--I don't know how the second sentence in the note is supposed to read, and whether it suggests something different--><!--from what the Spring developers suggest, or is it the same thing? Clarify. TR: Revised.--></para>

      <para>However, if you are getting measurable value from using the RDBMS
      operation classes, continue using these classes.</para>
    </note>

    <section id="jdbc-SqlQuery">
      <title><classname>SqlQuery</classname></title>

      <para><classname>SqlQuery</classname> is a reusable, threadsafe class
      that encapsulates an SQL query. Subclasses must implement the
      <methodname>newRowMapper(..)</methodname> method to provide a
      <interfacename>RowMapper</interfacename> instance that can create one
      object per row obtained from iterating over the
      <interfacename>ResultSet</interfacename> that is created during the
      execution of the query. The <classname>SqlQuery</classname> class is
      rarely used directly because the <classname>MappingSqlQuery</classname>
      subclass provides a much more convenient implementation for mapping rows
      to Java classes. Other implementations that extend
      <classname>SqlQuery</classname> are
      <classname>MappingSqlQueryWithParameters</classname> and
      <classname>UpdatableSqlQuery</classname>.</para>
    </section>

    <section id="jdbc-MappingSqlQuery">
      <title><classname>MappingSqlQuery</classname></title>

      <para><classname>MappingSqlQuery</classname> is a reusable query in
      which concrete subclasses must implement the abstract
      <methodname>mapRow(..)</methodname> method to convert each row of the
      supplied <interfacename>ResultSet</interfacename> into an object of the
      type specified. The following example shows a custom query that maps the
      data from the <code>t_actor</code> relation to an instance of the
      <classname>Actor</classname> class.</para>

      <programlisting language="java">public class ActorMappingQuery extends MappingSqlQuery&lt;Actor&gt; {

    public ActorMappingQuery(DataSource ds) {
        super(ds, "select id, first_name, last_name from t_actor where id = ?");
        super.declareParameter(new SqlParameter("id", Types.INTEGER));
        compile();
    }

    @Override
    protected Actor mapRow(ResultSet rs, int rowNumber) throws SQLException {
        Actor actor = new Actor();
        actor.setId(rs.getLong("id"));
        actor.setFirstName(rs.getString("first_name"));
        actor.setLastName(rs.getString("last_name"));
        return actor;
    }

}</programlisting>

      <para>The class extends <classname>MappingSqlQuery</classname>
      parameterized with the <classname>Actor</classname> type. The
      constructor for this customer query takes the
      <interfacename>DataSource</interfacename> as the only parameter. In this
      constructor you call the constructor on the superclass with the
      <interfacename>DataSource</interfacename> and the SQL that should be
      executed to retrieve the rows for this query. This SQL will be used to
      create a <interfacename>PreparedStatement</interfacename> so it may
      contain place holders for any parameters to be passed in during
      execution.<!--Identify *it*. PreparedStatement? TR: It's a common Java JDBC class.-->You
      must declare each parameter using the
      <literal>declareParameter</literal> method passing in an
      <classname>SqlParameter</classname>. <!--Rewording ok? Whenever you say that X *must* happen, it usually involves human interaction to make X happen or do something to --><!--make X happen. TR: Revised.-->The
      <classname>SqlParameter</classname> takes a name and the JDBC type as
      defined in <classname>java.sql.Types</classname>. After you define all
      parameters, you call the <literal>compile()</literal> method so the
      statement can be prepared and later executed. This class is thread-safe
      after it is compiled, so as long as these instances<!--beginning of sentence says *this class*, then it says *these classes*. Are you talking about one class or multiple classes. Revise. TR: Revised.-->
      are created when the DAO is initialized they can be kept as instance
      variables and be reused.</para>

      <programlisting language="java">private ActorMappingQuery actorMappingQuery;

@Autowired
public void setDataSource(DataSource dataSource) {
    this.actorMappingQuery = new ActorMappingQuery(dataSource);
}

public Customer getCustomer(Long id) {
    return actorMappingQuery.findObject(id);
}</programlisting>

      <para>The method in this example retrieves the customer with the id that
      is passed in as the only parameter. Since we only want one object
      returned we simply call the convenience method <code>findObject</code>
      with the id as parameter. If we had instead a query that returned a list
      of objects and took additional parameters then we would use one of the
      execute methods that takes an array of parameter values passed in as
      varargs.</para>

      <programlisting language="java">public List&lt;Actor&gt; searchForActors(int age, String namePattern) {
    List&lt;Actor&gt; actors = actorSearchMappingQuery.execute(age, namePattern);
    return actors;
}</programlisting>
    </section>

    <section id="jdbc-SqlUpdate">
      <title><classname>SqlUpdate</classname></title>

      <para>The <classname>SqlUpdate</classname> class encapsulates an SQL
      update. Like a query, an update object is reusable, and like all
      <classname>RdbmsOperation</classname> classes, an update can have
      parameters and is defined in SQL. This class provides a number of
      <methodname>update(..)</methodname> methods analogous to the
      <methodname>execute(..)</methodname> methods of query objects. The
      <classname>SQLUpdate</classname> class is concrete. It can be
      subclassed, for example, to add a custom update method, as in the
      following snippet where it's simply called
      <classname>execute</classname>. <!--I have broken the preceding line and next line into two sentences, but they still don't read right. What do you mean by *where we call it--><!--execute*? That doesn't make sense. Also, avoid *we*, say *you*. TR: revised.-->However,
      you don't have to subclass the <classname>SqlUpdate</classname> class
      since it can easily be parameterized by setting SQL and declaring
      parameters.<!--Revise *parameterized*; this is not a word. And, what is the point being made? Rewrite this sentence and the one before it. TR: OK.--></para>

      <programlisting language="java">import java.sql.Types;

import javax.sql.DataSource;

import org.springframework.jdbc.core.SqlParameter;
import org.springframework.jdbc.object.SqlUpdate;

public class UpdateCreditRating extends SqlUpdate {

    public UpdateCreditRating(DataSource ds) {
        setDataSource(ds);
        setSql("update customer set credit_rating = ? where id = ?");
        declareParameter(new SqlParameter("creditRating", Types.NUMERIC));
        declareParameter(new SqlParameter("id", Types.NUMERIC));
        compile();
    }

    /**
     * @param id for the Customer to be updated
     * @param rating the new value for credit rating
     * @return number of rows updated
     */
    public int execute(int id, int rating) {
        return update(rating, id);
    }
}</programlisting>
    </section>

    <section id="jdbc-StoredProcedure">
      <title><classname>StoredProcedure</classname></title>

      <para>The <classname>StoredProcedure</classname> class is a superclass
      for object abstractions of RDBMS stored procedures. This class is
      <literal>abstract</literal>, and its various
      <literal>execute(..)</literal> methods have <literal>protected</literal>
      access, preventing use other than through a subclass that offers tighter
      typing.</para>

      <para>The inherited <literal>sql</literal> property will be the name of
      the stored procedure in the RDBMS.</para>

      <para>To define a parameter for the
      <classname>StoredProcedure</classname> class, you use an
      <classname>SqlParameter</classname> or one of its subclasses. You must
      specify the parameter name and SQL type in the constructor like in the
      following code snippet. The SQL type is specified using the
      <classname>java.sql.Types</classname> constants.<!--The following example shows what, what is its purpose? TR: Revised.--></para>

      <para><programlisting language="java">   new SqlParameter("in_id", Types.NUMERIC),
   new SqlOutParameter("out_first_name", Types.VARCHAR),</programlisting></para>

      <para>The first line with the <classname>SqlParameter</classname>
      declares an IN parameter. IN parameters can be used for both stored
      procedure calls and for queries using the
      <classname>SqlQuery</classname> and its subclasses covered in the
      following section.</para>

      <para>The second line with the <classname>SqlOutParameter</classname>
      declares an <code>out</code> parameter to be used in the stored
      procedure call. There is also an
      <classname>SqlInOutParameter</classname> for
      <code>I</code><code>nOut</code> parameters, parameters that provide an
      <code>in</code> value to the procedure and that also return a
      value.</para>

      <para>For <code>i</code><code>n</code> parameters, in addition to the
      name and the SQL type, you can specify a scale for numeric data or a
      type name for custom database types. For <code>out</code> parameters you
      can provide a <classname>RowMapper</classname> to handle mapping of rows
      returned from a REF cursor. Another option is to specify an
      <classname>SqlReturnType</classname> that enables you to define
      customized handling of the return values.</para>

      <para>Here is an example of a simple DAO that uses a
      <classname>StoredProcedure</classname> to call a function,
      <literal>sysdate()</literal>,which comes with any Oracle database. To
      use the stored procedure functionality you have to create a class that
      extends <classname>StoredProcedure</classname>. In this example, the
      <classname>StoredProcedure</classname> class is an inner class, but if
      you need to reuse the <classname>StoredProcedure</classname> you declare
      it as a top-level class. This example has no input parameters, but an
      output parameter is declared as a date type using the class
      <classname>SqlOutParameter</classname>. The <literal>execute()</literal>
      method executes the procedure and extracts the returned date from the
      results <classname>Map</classname>. The results
      <classname>Map</classname> has an entry for each declared output
      parameter, in this case only one, using the parameter name as the
      key.</para>

      <programlisting language="java">import java.sql.Types;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.object.StoredProcedure;

public class StoredProcedureDao {

    private GetSysdateProcedure getSysdate;
    
    @Autowired
    public void init(DataSource dataSource) {
        this.getSysdate = new GetSysdateProcedure(dataSource);
    }
    
    public Date getSysdate() {
        return getSysdate.execute();
    }

    private class GetSysdateProcedure extends StoredProcedure {
        
        private static final String SQL = "sysdate";

        public GetSysdateProcedure(DataSource dataSource) {
            setDataSource(dataSource);
            setFunction(true);
            setSql(SQL);
            declareParameter(new SqlOutParameter("date", Types.DATE));
            compile();
        }

        public Date execute() {
            // the 'sysdate' sproc has no input parameters, so an empty Map is supplied...
            Map&lt;String, Object&gt; results = execute(new HashMap&lt;String, Object&gt;());
            Date sysdate = (Date) results.get("date");
            return sysdate;    
        }
    }

}</programlisting>

      <para>The following example of a <classname>StoredProcedure</classname>
      has two output parameters (in this case, Oracle REF cursors).</para>

      <programlisting language="java">import oracle.jdbc.OracleTypes;
import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.object.StoredProcedure;

import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;

public class TitlesAndGenresStoredProcedure extends StoredProcedure {

    private static final String SPROC_NAME = "AllTitlesAndGenres";

    public TitlesAndGenresStoredProcedure(DataSource dataSource) {
        super(dataSource, SPROC_NAME);
        declareParameter(new SqlOutParameter("titles", OracleTypes.CURSOR, new TitleMapper()));
        declareParameter(new SqlOutParameter("genres", OracleTypes.CURSOR, new GenreMapper()));
        compile();
    }

    public Map&lt;String, Object&gt; execute() {
        // again, this sproc has no input parameters, so an empty Map is supplied
        return super.execute(new HashMap&lt;String, Object&gt;());
    }
}</programlisting>

      <para>Notice how the overloaded variants of the
      <literal>declareParameter(..)</literal> method that have been used in
      the <classname>TitlesAndGenresStoredProcedure</classname> constructor
      are passed <interfacename>RowMapper</interfacename> implementation
      instances; this is a very convenient and powerful way to reuse existing
      functionality. The code for the two
      <interfacename>RowMapper</interfacename> implementations is provided
      below.</para>

      <para>The <classname>TitleMapper</classname> class maps a
      <interfacename>ResultSet</interfacename> to a
      <classname>Title</classname> domain object for each row in the supplied
      <interfacename>ResultSet</interfacename>:</para>

      <programlisting language="java">import org.springframework.jdbc.core.RowMapper;

import java.sql.ResultSet;
import java.sql.SQLException;

import com.foo.domain.Title;

public final class TitleMapper implements RowMapper&lt;Title&gt; {
    
    public Title mapRow(ResultSet rs, int rowNum) throws SQLException {
        Title title = new Title();
        title.setId(rs.getLong("id"));
        title.setName(rs.getString("name"));
        return title;
    }
}</programlisting>

      <para>The <classname>GenreMapper</classname> class maps a
      <interfacename>ResultSet</interfacename> to a
      <classname>Genre</classname> domain object for each row in the supplied
      <interfacename>ResultSet</interfacename>.</para>

      <programlisting language="java">import org.springframework.jdbc.core.RowMapper;

import java.sql.ResultSet;
import java.sql.SQLException;

import com.foo.domain.Genre;

public final class GenreMapper implements RowMapper&lt;Genre&gt; {
    
    public Genre mapRow(ResultSet rs, int rowNum) throws SQLException {
        return new Genre(rs.getString("name"));
    }
}</programlisting>

      <para>To pass parameters to a stored procedure that has one or more
      input parameters in its definition in the RDBMS, you can code a strongly
      typed <literal>execute(..)</literal> method that would delegate to the
      superclass' untyped <literal>execute(Map parameters)</literal> method
      (which has <literal>protected</literal> access); <!--Wording of preceding line is very awkward and doesn't track well at all. Please revise. Don't overuse parentheses. TR: Revised.-->for
      example:</para>

      <programlisting language="java">import oracle.jdbc.OracleTypes;
import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.core.SqlParameter;
import org.springframework.jdbc.object.StoredProcedure;

import javax.sql.DataSource;

import java.sql.Types;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

public class TitlesAfterDateStoredProcedure extends StoredProcedure {

    private static final String SPROC_NAME = "TitlesAfterDate";
    private static final String CUTOFF_DATE_PARAM = "cutoffDate";

    public TitlesAfterDateStoredProcedure(DataSource dataSource) {
        super(dataSource, SPROC_NAME);
        declareParameter(new SqlParameter(CUTOFF_DATE_PARAM, Types.DATE);
        declareParameter(new SqlOutParameter("titles", OracleTypes.CURSOR, new TitleMapper()));
        compile();
    }

    public Map&lt;String, Object&gt; execute(Date cutoffDate) {
        Map&lt;String, Object&gt; inputs = new HashMap&lt;String, Object&gt;();
        inputs.put(CUTOFF_DATE_PARAM, cutoffDate);
        return super.execute(inputs);
    }
}</programlisting>
    </section>
  </section>

  <section id="jdbc-parameter-handling">
    <title>Common problems with parameter and data value handling</title>

    <para>Common problems with parameters and data values exist in the
    different approaches provided by the Spring Framework JDBC.</para>

    <section id="jdbc-type-information">
      <title>Providing SQL type information for parameters</title>

      <para>Usually Spring determines the SQL type of the parameters based on
      the type of parameter passed in. It is possible to explicitly provide
      the SQL type to be used when setting parameter values. This is sometimes
      necessary to correctly set NULL values.</para>

      <para>You can provide SQL type information in several ways:</para>

      <itemizedlist>
        <listitem>
          <para>Many update and query methods of the
          <classname>JdbcTemplate</classname> take an additional parameter in
          the form of an <code>int </code>array. This array is used to
          indicate the SQL type of the coresponding parameter using constant
          values from the <classname>java.sql.Types</classname> class. <!--Reword to say *what* is using constant values from the java.sql.Types class to do *what*. Phrases that being with *using* are --><!--often unclear as to what uses what to do what.-->Provide
          one entry for each parameter.</para>
        </listitem>
      </itemizedlist>

      <itemizedlist>
        <listitem>
          <para>You can use the <classname>SqlParameterValue</classname> class
          to wrap the parameter value that needs this additional information.
          <!--I revised another unclear case of *using*. If it's not correct, revise to say what is using the SqlParameterValue class to do what. TR: OK.-->Create
          a new instance for each value and pass in the SQL type and parameter
          value in the constructor. You can also provide an optional scale
          parameter for numeric values.</para>
        </listitem>
      </itemizedlist>

      <itemizedlist>
        <listitem>
          <para>For methods working with named parameters, use the
          <classname>SqlParameterSource</classname> classes
          <classname>BeanPropertySqlParameterSource</classname> or
          <classname>MapSqlParameterSource</classname>. They both have methods
          for registering the SQL type for any of the named parameter
          values.</para>
        </listitem>
      </itemizedlist>
    </section>

    <section id="jdbc-lob">
      <title>Handling BLOB and CLOB objects</title>

      <para>You can store images, other binary objects, and large chunks of
      text. These large object are called BLOB for binary data and CLOB for
      character data. In Spring you can handle these large objects by using
      the JdbcTemplate directly and also when using the higher abstractions
      provided by RDBMS Objects and the <code>SimpleJdbc</code> classes. All
      of these approaches use an implementation of the
      <classname>LobHandler</classname> interface for the actual management of
      the LOB data. The <classname>LobHandler</classname> provides access to a
      <classname>LobCreator</classname> class, through the
      <classname>getLobCreator</classname> method, used for creating new LOB
      objects to be inserted.</para>

      <para>The <classname>LobCreator/LobHandler</classname> provides the
      following support for LOB input and output:</para>

      <para><itemizedlist>
          <listitem>
            <para>BLOB</para>

            <itemizedlist>
              <listitem>
                <para>byte[] – getBlobAsBytes and setBlobAsBytes</para>
              </listitem>

              <listitem>
                <para>InputStream – getBlobAsBinaryStream and
                setBlobAsBinaryStream</para>
              </listitem>
            </itemizedlist>
          </listitem>
        </itemizedlist><itemizedlist>
          <listitem>
            <para>CLOB</para>

            <itemizedlist>
              <listitem>
                <para>String – getClobAsString and setClobAsString</para>
              </listitem>

              <listitem>
                <para>InputStream – getClobAsAsciiStream and
                setClobAsAsciiStream</para>
              </listitem>

              <listitem>
                <para>Reader – getClobAsCharacterStream and
                setClobAsCharacterStream</para>
              </listitem>
            </itemizedlist>
          </listitem>
        </itemizedlist></para>

      <para>The next example shows how to create and insert a BLOB. Later you
      will see how to read it back from the database.</para>

      <para>This example uses a <code>JdbcTemplate</code> and an
      implementation of the
      <code>AbstractLobCreatingPreparedStatementCallbac</code><code>k</code>.
      It implements one method, <code>setValues</code>. This method provides a
      <code>LobCreator</code> that you use to set the values for the LOB
      columns in your SQL insert statement.</para>

      <para>For this example we assume that there is a variable,
      <code>lobHandle</code><code>r</code>, that already is set to an instance
      of a <classname>DefaultLobHandler</classname>. You typically set this
      value through dependency injection.<!--Rewording ok? (What does what through dependency injection?) TR: Revised.--></para>

      <programlistingco>
        <areaspec>
          <area coords="8" id="jdbc.lobhandler.variableref" />

          <area coords="12" id="jdbc.lobhandler.setClob" />

          <area coords="13" id="jdbc.lobhandler.setBlob" />
        </areaspec>

        <programlisting language="java">final File blobIn = new File("spring2004.jpg");
final InputStream blobIs = new FileInputStream(blobIn);
final File clobIn = new File("large.txt");
final InputStream clobIs = new FileInputStream(clobIn);
final InputStreamReader clobReader = new InputStreamReader(clobIs);
jdbcTemplate.execute(
  "INSERT INTO lob_table (id, a_clob, a_blob) VALUES (?, ?, ?)",
  new AbstractLobCreatingPreparedStatementCallback(lobHandler) {
      protected void setValues(PreparedStatement ps, LobCreator lobCreator) 
          throws SQLException {
        ps.setLong(1, 1L);
        lobCreator.setClobAsCharacterStream(ps, 2, clobReader, (int)clobIn.length());
        lobCreator.setBlobAsBinaryStream(ps, 3, blobIs, (int)blobIn.length());
      }
  }
);
blobIs.close();
clobReader.close();</programlisting>

        <calloutlist>
          <callout arearefs="jdbc.lobhandler.variableref">
            <para>Pass in the lobHandler that in this example is a plain
            <classname>DefaultLobHandler</classname><!--*Here* where?(deleted *Here we*) I don't see this in example.Use the lobHandler to do what? TR: Revised.--></para>
          </callout>

          <callout arearefs="jdbc.lobhandler.setClob">
            <para>Using the method
            <classname>setClobAsCharacterStream</classname>, pass in the
            contents of the CLOB.</para>
          </callout>

          <callout arearefs="jdbc.lobhandler.setBlob">
            <para>Using the method
            <classname>setBlobAsBinaryStream</classname>, pass in the contents
            of the BLOB.</para>
          </callout>
        </calloutlist>
      </programlistingco>

      <para>Now it's time to read the LOB data from the database. Again, you
      use a <code>JdbcTemplate</code> with the same instance variable
      <code>l</code><code>obHandler </code>and a reference to a
      <classname>DefaultLobHandler</classname>.</para>

      <para><programlistingco>
          <areaspec>
            <area coords="5" id="jdbc.lobhandler.getClob" />

            <area coords="7" id="jdbc.lobhandler.getBlob" />
          </areaspec>

          <programlisting language="java">List&lt;Map&lt;String, Object&gt;&gt; l = jdbcTemplate.query("select id, a_clob, a_blob from lob_table",
        new RowMapper&lt;Map&lt;String, Object&gt;&gt;() {
          public Map&lt;String, Object&gt; mapRow(ResultSet rs, int i) throws SQLException {
            Map&lt;String, Object&gt; results = new HashMap&lt;String, Object&gt;();
            String clobText = lobHandler.getClobAsString(rs, "a_clob");
            results.put("CLOB", clobText);
            byte[] blobBytes = lobHandler.getBlobAsBytes(rs, "a_blob");
            results.put("BLOB", blobBytes);
            return results;
          }
        });
</programlisting>

          <calloutlist>
            <callout arearefs="jdbc.lobhandler.setClob">
              <para>Using the method <classname>getClobAsString,
              </classname>retrieve the contents of the CLOB.</para>
            </callout>

            <callout arearefs="jdbc.lobhandler.setBlob">
              <para>Using the method <classname>getBlobAsBytes,</classname>
              retrieve the contents of the BLOB.<!--MISSING THE NUMBER 2 IN SNIPPET ABOVE. ADD WHERE APPROPRIATE. TR: ?; OK AS IS.--></para>
            </callout>
          </calloutlist>
        </programlistingco></para>
    </section>

    <section id="jdbc-in-clause">
      <title>Passing in lists of values for IN clause</title>

      <para>The SQL standard allows for selecting rows based on an expression
      that includes a variable list of values. A typical example would be
      <code>select * from T_ACTOR where id in (1, 2, 3)</code>. This variable
      list is not directly supported for prepared statements by the JDBC
      standard; you cannot declare a variable number of placeholders. You need
      a number of variations with the desired number of placeholders prepared,
      or you need to generate the SQL string dynamically once you know how
      many placeholders are required. The named parameter support provided in
      the <classname>NamedParameterJdbcTemplate</classname> and
      <classname>SimpleJdbcTemplate</classname> takes the latter approach.
      Pass in the values as a <classname>java.util.List</classname> of
      primitive objects. This list will be used to insert the required
      placeholders and pass in the values during the statement
      execution.</para>

      <note>
        <para>Be careful when passing in many values. The JDBC standard does
        not guarantee that you can use more than 100 values for an
        <code>in</code> expression list. Various databases exceed this number,
        but they usually have a hard limit for how many values are allowed.
        Oracle's limit is 1000.</para>
      </note>

      <para>In addition to the primitive values in the value list, you can
      create a <classname>java.util.List</classname> of object arrays. This
      list would support multiple expressions defined for the <code>in</code>
      clause such as <code>select * from T_ACTOR where (id, last_name) in
      ((1, 'Johnson'), (2, 'Harrop'))</code>. This
      of course requires that your database supports this syntax.</para>
    </section>

    <section id="jdbc-complex-types">
      <title>Handling complex types for stored procedure calls</title>

      <para>When you call stored procedures you can sometimes use complex
      types specific to the database. To accommodate these types, Spring
      provides a <classname>SqlReturnType</classname> for handling them when
      they are returned from the stored procedure call and
      <classname>SqlTypeValue</classname> when they are passed in as a
      parameter to the stored procedure.</para>

      <para>Here is an example of returning the value of an Oracle
      <code>STRUCT</code> object of the user declared type
      <code>ITEM_TYPE</code>. The <classname>SqlReturnType</classname>
      interface has a single method named <classname>getTypeValue</classname>
      that must be implemented. This interface is used as part of the
      declaration of an <classname>SqlOutParameter</classname>.</para>

      <para><programlisting language="java">final TestItem - new TestItem(123L, "A test item", 
        new SimpleDateFormat("yyyy-M-d").parse("2010-12-31"););

declareParameter(new SqlOutParameter("item", OracleTypes.STRUCT, "ITEM_TYPE",
    new SqlReturnType() {
      public Object getTypeValue(CallableStatement cs, int colIndx, int sqlType, String typeName) 
          throws SQLException {
        STRUCT struct = (STRUCT)cs.getObject(colIndx);
        Object[] attr = struct.getAttributes();
        TestItem item = new TestItem();
        item.setId(((Number) attr[0]).longValue());
        item.setDescription((String)attr[1]);
        item.setExpirationDate((java.util.Date)attr[2]);
        return item;
      }
    }));</programlisting>You use the <classname>SqlTypeValue</classname> to
      pass in the value of a Java object like <classname>TestItem</classname>
      into a stored procedure. <!--Revise preceding as necessary. What do you mean by *go[ing] from Java to the database*? Is that the right way to say it? TR: Revised.-->The
      <classname>SqlTypeValue</classname> interface has a single method named
      <classname>createTypeValue</classname> that you must implement. The
      active connection is passed in, and you can use it to create
      database-specific objects such as
      <classname>StructDescriptor</classname>s, as shown in the following
      example, or <classname>ArrayDescriptor</classname>s.<!--Rewording of preceding ok? The example is showing human participation, I assume. ;-) TR: Yes :), OK.--></para>

      <para><programlisting language="java">final TestItem - new TestItem(123L, "A test item", 
        new SimpleDateFormat("yyyy-M-d").parse("2010-12-31"););

SqlTypeValue value = new AbstractSqlTypeValue() {
  protected Object createTypeValue(Connection conn, int sqlType, String typeName) throws SQLException {
    StructDescriptor itemDescriptor = new StructDescriptor(typeName, conn);
    Struct item = new STRUCT(itemDescriptor, conn,
        new Object[] {
            testItem.getId(),
            testItem.getDescription(),
            new java.sql.Date(testItem.getExpirationDate().getTime())
        });
    return item;
  }
};</programlisting>This <classname>SqlTypeValue</classname> can now be added
      to the Map containing the input parameters for the execute call of the
      stored procedure.</para>

      <para>Another use for the <classname>SqlTypeValue</classname> is passing
      in an array of values to an Oracle stored procedure. Oracle has its own
      internal <classname>ARRAY</classname> class that must be used in this
      case, and you can use the <classname>SqlTypeValue</classname> to create
      an instance of the Oracle <classname>ARRAY</classname> and populate it
      with values from the Java <code>ARRAY</code>.</para>

      <programlisting language="java">final Long[] ids = new Long[] {1L, 2L};

SqlTypeValue value = new AbstractSqlTypeValue() {
  protected Object createTypeValue(Connection conn, int sqlType, String typeName) throws SQLException {
    ArrayDescriptor arrayDescriptor = new ArrayDescriptor(typeName, conn);
    ARRAY idArray = new ARRAY(arrayDescriptor, conn, ids);
    return idArray;
  }
};</programlisting>
    </section>
  </section>

  <section id="jdbc-embedded-database-support">
    <title>Embedded database support</title>

    <para>The <literal>org.springframework.jdbc.datasource.embedded</literal>
    package provides support for embedded Java database engines. Support for
    <ulink url="http://www.hsqldb.org">HSQL</ulink>, <ulink
    url="http://www.h2database.com">H2</ulink>, and <ulink
    url="http://db.apache.org/derby">Derby</ulink> is provided natively. You
    can also use an extensible API to plug in new embedded database types and
    <classname>DataSource</classname> implementations.</para>

    <section id="jdbc-why-embedded-database">
      <title>Why use an embedded database?</title>

      <para>An embedded database is useful during the development phase of a
      project because of its lightweight nature. Benefits include ease of
      configuration, quick startup time, testability, and the ability to
      rapidly evolve SQL during development.</para>
    </section>

    <section id="jdbc-embedded-database-xml">
      <title>Creating an embedded database instance using Spring XML</title>

      <para>If you want to expose an embedded database instance as a bean in a
      Spring ApplicationContext, use the embedded-database tag in the
      spring-jdbc namespace: <programlisting language="xml">    &lt;jdbc:embedded-database id="dataSource"&gt;
        &lt;jdbc:script location="classpath:schema.sql"/&gt;
        &lt;jdbc:script location="classpath:test-data.sql"/&gt;
    &lt;/jdbc:embedded-database&gt;
</programlisting></para>

      <para>The preceding configuration creates an embedded HSQL database
      populated with SQL from schema.sql and testdata.sql resources in the
      classpath. The database instance is made available to the Spring
      container as a bean of type <classname>javax.sql.DataSource</classname>.
      This bean can then be injected into data access objects as
      needed.</para>
    </section>

    <section id="jdbc-embedded-database-java">
      <title>Creating an embedded database instance programmatically</title>

      <para>The <classname>EmbeddedDatabaseBuilder</classname> class provides
      a fluent API for constructing an embedded database programmatically. Use
      this when you need to create an embedded database instance in a
      standalone environment, such as a data access object unit test:
      <programlisting language="java">    EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder();
    EmbeddedDatabase db = builder.setType(H2).addScript("my-schema.sql").addScript("my-test-data.sql").build();
    // do stuff against the db (EmbeddedDatabase extends javax.sql.DataSource)
    db.shutdown()
</programlisting></para>
    </section>

    <section id="jdbc-embedded-database-extension">
      <title>Extending the embedded database support</title>

      <para>Spring JDBC embedded database support can be extended in two ways:
      <orderedlist>
          <listitem>
            <para>Implement <classname>EmbeddedDatabaseConfigurer</classname>
            to support a new embedded database type, such as Apache
            Derby.</para>
          </listitem>

          <listitem>
            <para>Implement <classname>DataSourceFactory</classname> to
            support a new DataSource implementation, such as a connection
            pool, to manage embedded database connections.</para>
          </listitem>
        </orderedlist></para>

      <para>You are encouraged to contribute back extensions to the Spring
      community at <ulink
      url="jira.springframework.org">jira.springframework.org</ulink>.</para>
    </section>

    <section id="jdbc-embedded-database-using-HSQL">
      <title>Using HSQL</title>

      <para>Spring supports HSQL 1.8.0 and above. HSQL is the default embedded
      database if no type is specified explicitly. To specify HSQL explicitly, 
      set the <literal>type</literal> attribute of the
      <literal>embedded-database</literal> tag to <literal>HSQL</literal>. If
      you are using the builder API, call the
      <literal>setType(EmbeddedDatabaseType)</literal> method with
      <literal>EmbeddedDatabaseType.HSQL</literal>.</para>
    </section>

    <section id="jdbc-embedded-database-using-H2">
      <title>Using H2</title>

      <para>Spring supports the H2 database as well. To enable H2, set the
      <literal>type</literal> attribute of the
      <literal>embedded-database</literal> tag to <literal>H2</literal>. If
      you are using the builder API, call the
      <literal>setType(EmbeddedDatabaseType)</literal> method with
      <literal>EmbeddedDatabaseType.H2</literal>.</para>
    </section>

    <section id="jdbc-embedded-database-using-Derby">
      <title>Using Derby</title>

      <para>Spring also supports Apache Derby 10.5 and above. To enable Derby,
      set the <literal>type</literal> attribute of the
      <literal>embedded-database</literal> tag to <literal>Derby</literal>. If
      using the builder API, call the
      <literal>setType(EmbeddedDatabaseType)</literal> method with
      <literal>EmbeddedDatabaseType.Derby</literal>.</para>
    </section>

    <section id="jdbc-embedded-database-dao-testing">
      <title>Testing data access logic with an embedded database</title>

      <para>Embedded databases provide a lightweight way to test data access
      code. The following is a data access unit test template that uses an
      embedded database:</para>

      <programlisting language="java">
public class DataAccessUnitTestTemplate {
    private EmbeddedDatabase db;
    
    @Before
    public void setUp() {
        // creates a HSQL in-memory db populated from default scripts classpath:schema.sql and classpath:test-data.sql
        db = new EmbeddedDatabaseBuilder().addDefaultScripts().build();		
    }

    @Test
    public void testDataAccess() {
        JdbcTemplate template = new JdbcTemplate(db);
        template.query(...);
    }

    @After
    public void tearDown() {
        db.shutdown();
    }
}
</programlisting>
    </section>
  </section>

  <section>
    <title>Initializing a DataSource</title>

    <para>The <literal>org.springframework.jdbc.datasource.init</literal>
    package provides support for initializing an existing
    <classname>DataSource</classname>. The embedded database support provides
    one option for creating and initializing a
    <classname>DataSource</classname> for an application, but sometimes you
    need to initialize an instance running on a server somewhere.</para>

    <section>
      <title>Initializing a database instance using Spring XML</title>

      <para>If you want to initialize a database and you can provide a
      reference to a DataSource bean, use the
      <literal>initialize-database</literal> tag in the
      <literal>spring-jdbc</literal> namespace:</para>

      <programlisting>&lt;jdbc:initialize-database data-source="dataSource"&gt;
  &lt;jdbc:script location="classpath:com/foo/sql/db-schema.sql"/&gt;
  &lt;jdbc:script location="classpath:com/foo/sql/db-test-data.sql"/&gt;
&lt;/jdbc:initialize-database&gt;</programlisting>

      <para>The example above runs the two scripts specified against the
      database: the first script is a schema creation, and the second is a
      test data set insert. The script locations can also be patterns with
      wildcards in the usual ant style used for resources in Spring (e.g.
      <code>classpath*:/com/foo/**/sql/*-data.sql</code>). If a pattern is
      used the scripts are executed in lexical order of their URL or
      filename.</para>

      <para>The default behaviour of the database initializer is to
      unconditionally execute the scripts provided. This will not always be
      what you want, for instance if running against an existing database that
      already has test data in it. The likelihood of accidentally deleting
      data is reduced by the commonest pattern (as shown above) that creates
      the tables first and then inserts the data - the first step will fail if
      the tables already exist.</para>

      <para>However, to get more control over the creation and deletion of
      existing data, the XML namespace provides a couple more options. The
      first is flag to switch the initialization on and off. This can be set
      according to the environment (e.g. to pull a boolean value from system
      properties or an environment bean), e.g.
      <programlisting>&lt;jdbc:initialize-database data-source="dataSource"
    <emphasis role="bold">enabled="#{systemProperties.INITIALIZE_DATABASE}"</emphasis>&gt;
  &lt;jdbc:script location="..."/&gt;
&lt;/jdbc:initialize-database&gt;</programlisting></para>

      <para>The second option to control what happens with existing data is to
      be more tolerant of failures. To this end you can control the ability of
      the initializer to ignore certain errors in the SQL it executes from the
      scripts, e.g.</para>

      <para><programlisting>&lt;jdbc:initialize-database data-source="dataSource" <emphasis
            role="bold">ignore-failures="DROPS"</emphasis>&gt;
  &lt;jdbc:script location="..."/&gt;
&lt;/jdbc:initialize-database&gt;</programlisting>In this example we are
      saying we expect that sometimes the scripts will be run against an empty
      dtabase and there are some DROP statements in the scripts which would
      therefore fail. So failed SQL <code>DROP</code> statements will be
      ignored, but other failures will cause an exception. This is useful if
      your SQL dialect doesn't support <code>DROP ... IF EXISTS</code> (or
      similar) but you want to unconditionally remove all test data before
      re-creating it. In that case the first script is usually a set of drops,
      followed by a set of <code>CREATE</code> statements.</para>

      <para>The <code>ignore-failures</code> option can be set to
      <code>NONE</code> (the default), <code>DROPS</code> (ignore failed
      drops) or <code>ALL</code> (ignore all failures).</para>

      <para>If you need more control than you get from the XML namespace, you
      can simply use the <classname>DataSourceInitializer</classname>
      directly, and define it as a component in your application.</para>

      <section>
        <title>Initialization of Other Components that Depend on the
        Database</title>

        <para>A large class of applications can just use the database
        initializer with no further complications: those that do not use the
        database until after the Spring context has started. If your
        application is <emphasis>not</emphasis> one of those then you might
        need to read the rest of this section.</para>

        <para>The database initializer depends on a data source instance and
        runs the scripts provided in its initialization callback (c.f.
        <code>init-method</code> in an XML bean definition or
        <code>InitializingBean</code>). If other beans depend on the same data
        source and also use the data source in an initialization callback then
        there might be a problem because the data has not yet been
        initialized. A common example of this is a cache that initializes
        eagerly and loads up data from the database on application
        startup.</para>

        <para>To get round this issue you two options: change your cache
        initialization strategy to a later phase, or ensure that the database
        initializer is initialized first.</para>

        <para>The first option might be easy if the application is in your
        control, and not otherwise. Some suggestions for how to implement this
        are<itemizedlist>

            <listitem>
              <para>Make the cache initialize lazily on first usage, which
              improves application startup time</para>
            </listitem>

            <listitem>
              <para>Have your cache or a separate component that
              initializes the cache implement <code>Lifecycle</code> or 
              <code>SmartLifecycle</code>.  When the application context
              starts up a <code>SmartLifecycle</code> can be automatically
              started if its <code>autoStartup</code> flag is set, 
              and a <code>Lifecycle</code> can be started
              manually by calling 
              <code>ConfigurableApplicationContext.start()</code> on the
              enclosing context.
              </para>
            </listitem>

            <listitem>
              <para>Use a Spring <code>ApplicationEvent</code> or similar
              custom observer mechanism to trigger the cache initialization.
              <code>ContextRefreshedEvent</code> is always published by the
              context when it is ready for use (after all beans have been
              initialized), so that is often a useful hook (this is
              how the <code>SmartLifecycle</code> works by default).</para>
            </listitem>

          </itemizedlist></para>

        <para>The second option can also be easy. Some suggestions on how to
        implement this are<itemizedlist>
            <listitem>
              <para>Rely on Spring BeanFactory default behaviour, which is
              that beans are initialized in registration order. You can easily
              arrange that by adopting the common practice of a set of
              &lt;import/&gt; elements that order your application modules,
              and ensure that the database and database initialization are
              listed first</para>
            </listitem>

            <listitem>
              <para>Separate the datasource and the business components that
              use it and control their startup order by putting them in
              separate ApplicationContext instances (e.g. parent has the
              datasource and child has the business components). This
              structure is common in Spring web applications, but can be more
              generally applied.</para>
            </listitem>

            <listitem>
              <para>Use a modular runtime like SpringSource dm Server and
              separate the data source and the components that depend on it.
              E.g. specify the bundle start up order as datasource -&gt;
              initializer -&gt; business components.</para>
            </listitem>
          </itemizedlist></para>
      </section>
    </section>
  </section>
</chapter>